Studienarbeit Nr. 2275
Concept and Implementation of
a Graphical Editor for
Composite Application Templates
Xuan Wang Studiengang: Prüfer: begonnen am: beendet am: CR-Klassifikation: Betreuer: Informatik
Prof. Dr. Frank Leymann Dipl. -Inf. Ralph Mietzner 01.11.2009 03.05.2010 C.2.4, D.2.6 Universität Stuttgart Universitätsstraße 38 D - 70569 Stuttgart
Table of Contents
1 Introduction ... 3 1.1 Task ... 3 1.2 Structure ... 3 2 Cloud Computing ... 5 2.1 Definition and History of Cloud Computing ... 5 2.2 Three Levels of Cloud Platforms ... 5 2.3 Economics of Cloud Computing ... 9 2.4 Advantages and Risks ... 11 2.5 Component‐Based Application Design ... 133 Composite Application Framework ... 15
3.1 Introduction ... 15
3.2 Features of Composite Application Framework... 15
3.3 Cafe Project ... 16
4 Eclipse Modeling Projects and Plug-In ... 24
4.1 Introduction and Background ... 24
4.2 Eclipse Modeling Framework (EMF) ... 25
4.3 Graphic Editing Framework (GEF) ... 27
4.4 Graphic Modeling Framework (GMF) ... 29
4.5 Plug‐In Development Environment (PDE) ... 31
5 Implementation of Graphical Editor ... 32
5.1 Installation of GMF ... 32 5.2 Ecore Model ... 33 5.3 Graphical Definition Model ... 36 5.4 Tooling Definition Model ... 41 5.5 Mapping Model ... 42 5.6 Generator Model ... 45 5.7 Generate Diagram Code ... 46 5.8 GMF Runtime... 47 5.9 CAR File Export ... 53
6 Discussion and Outlook ... 63
6.1 Discussion ... 63
6.2 Outlook ... 63
7 Bibliography ... 64
Figure 2.1 Three Levels of Cloud Computing Structure………6 Figure 2.2 Infrastructure as a Service………..7 Figure 2.3 Platform as a Service………..8 Figure 2.4 Software as a Service………..9 Figure 3.1 Collapsed Example of Cafe Application………..17 Figure 3.2 Extended Example of Cafe Application………..18 Figure 3.3 Ecore Meta‐Model of Cafe Application………..19 Figure 3.4 Component Dependency………..19 Figure 3.5 Component Patterns………20 Figure 3.6 Deployment Relation………21 Figure 3.7 Implementations...21 Figure 3.8 Visible Property...22 Figure 3.9 Requirements...22 Figure 5.1 Create a New GMF Project with Eclipse New Wizard………32 Figure 5.2 Project Folder Structure...33 Figure 5.3 Ecore Model Diagram and Diagram Editor………34 Figure 5.4 Create Graphical Definition Model……….37 Figure 5.5 Figure Gallery...38 Figure 5.6 Rounded Rectangle Properties...39 Figure 5.7 Flow Layout Properties...39 Figure 5.8 Compartment Collapsible...41 Figure 5.9 Tool Palette...41 Figure 5.10 Canvas Mapping Properties...42 Figure 5.11 Top Node Reference...43 Figure 5.12 Node Mapping...43 Figure 5.13 Node Mapping Properties...44 Figure 5.14 Feature Label Mapping Properties………..44 Figure 5.15 Component Child Reference Properties………..45 Figure 5.16 Gen Editor Generator Properties……….46 Figure 5.17 Component Name Edit Part……….46 Figure 5.18 Cafe Application Editor………...48 Figure 5.19 Print………..49 Figure 5.20 View………..49 Figure 5.21 Page Breaks……….50 Figure 5.22 Example...51 Figure 5.23 Car Generator...54 Figure 5.24 Car File...55 Figure 5.25 Extensions...56
1 Introduction
1 Introduction
1.1 Task
Nowadays, Cloud Computing has raised a revolution in the whole IT environment. Plenty of large IT enterprises like IBM, Google, Microsoft and non‐IT enterprises like Amazon have invested a lot to deploy and propagate their Cloud Computing solutions. The traditional Cloud Computing solution is composed of service vendor/provider and services consumers, which delivers customer required infrastructures, software, application services and receive services through paying per usage. Those services received by customers, generally highly standardized, need customization or even redeployment by a third consultant company, which causes the overspending of IT‐budget and irregularly specified application services.
The Cafe project, based on Composite Application Framework, provides a new solution that separating the service vendor and service provider. Service vendor not only supports service provider at the level of infrastructure and application, but also provides a standard process. In order to meet the specified requirements of various customers, service provider should be capable of configuring and redeveloping the application. This kind of solution makes customers to acquire their own specified services through month‐based fees without configuration and redeployment by a third company.
The task of this student research project is to develop a graphical editor for Cafe application templates, which is based on Eclipse Graphic Modeling Framework (GMF) and implemented within Eclipse Plug‐In Development Environment (PDE). The editor is supposed to provide a user‐friendly GUI and allow exporting the Cafe application templates as a Cafe application archive file at the same time.
1.2 Structure
The Chapter 2 introduces three levels of Cloud Computing in details, the opportunity and risks in enterprise brought by Cloud Computing and Component‐based application design.
The Chapter 3 involves the composite application framework, the concepts and graphical implementation of Cafe application templates.
The Chapter 4 is concerned with background knowledge of Eclipse projects including Eclipse Modeling Framework (EMF), Graphic Editing Framework (GEF), Graphic Modeling Framework (GMF) and Plug‐In Development Environment (PDE).
Furthermore, it compares GMF with GEF.
The Chapter 5 covers the detailed implementation of graphical editor, GMF runtime and the implementation of .car file export.
2 Cloud Computing
2 Cloud
Computing
2.1 Definition and History of Cloud Computing
With the rapid development of Internet technology, Internet‐based applications are becoming more and more popular and significant. Under the circumstances, a new concept – Cloud Computing – springs up. Cloud Computing is not a new technology, but an integration of different existed technologies.
We define Cloud Computing as “an Internet‐based computing, where by shared resources, software and information are provided to computers and other devices on‐demand, like electricity.”[Clo] A more technical definition by National Institute of Standards and Technology (NIST) is that “the Cloud Computing is a computing capability that provides an abstraction between the computing resource and its underlying technical architecture (e.g., servers, storage, networks), enabling convenient, on‐demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction.”[MG09]
When Google raised the concept of Cloud Computing, Amazon had implemented Cloud Computing since 2005 by providing fees‐based access to their systems via Amazon Web Services. And also IBM, Intel and Sun declared that they had been already aware of the Cloud Computing since long. In my opinion, Cloud Computing is a further development of Distributed Computing, Parallel Computing and Grid Computing or to put it simply ‐ a commercialization of Grid Computing. The application area of Grid Computing, which has been widely applied for scientific computing or simulation among the research institutes, is limited to scientific scope and open source communities. As the scientific fulfillments can be looked as open sources for other scientists, there is no need to require a very high security mechanism. However, after the rapid growth of commercial environment requirements, those leading enterprises have made a lot of improvements to commercialize and widespread the Grid Computing technology.
2.2 Three Levels of Cloud Platforms
As described in Figure 2.1, there are three levels of Cloud platforms: Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and Software as a Service (SaaS), which will be elaborated in this Section.
Figure 2.1 Three Levels of Cloud Computing Structure
2.2.1 Infrastructure as a Service (IaaS)
IaaS is the bottom level abstracting the physical infrastructure. IaaS vendor provides the computing power, storage and other network infrastructures like firewalls for its customers, who purchase the software and hold the license. Further required is a runtime environment to implement their applications. Therefore, IaaS can also be seen as Hardware as a Service (HaaS).
Generally IaaS vendors provide services based on virtualization technology. IaaS customers should create a virtual machine with some operation system and other essential application software like database, web server and so on. After the installation and the configuration of applications, they have to upload the whole virtual machine image to the computer cluster provided by IaaS vendors. During the running of virtual machine, IaaS customers are responsible to the maintenances of the virtual machine, while IaaS vendors are responsible to the maintenances of provided infrastructures. The relationship among IaaS customers, Iaas vendors and end users is described in Figure 2.2.
2 Cloud Computing
Figure 2.2 Infrastructure as a Service
The service fees are based on performance usage such as the processing time, storage capacity, the bandwidth of the network etc. A practical example of IaaS products is Amazon Web Services. [Pij09]
To summarize, “Infrastructure‐as‐a‐service is about replacing critical data center resources such as space, pipe, firewalls, VPNs, routers, switches, physical servers and storage with scalable and highly‐available resources in the Cloud. It is about having a data‐center‐in‐the‐Cloud.”[CF08]
2.2.2 Platform as a Service (PaaS)
At the middle level stands the PaaS. PaaS vendors provide not only the computing power, storage and network infrastructures, but also the running environment as well as some Cloud services. PaaS customers occupy the application software and the license. What they need is a running environment to implement their applications just like IaaS customers.
End User
Customer
Configuration file or Application package
Figure 2.3 Platform as a Service
Figure 2.3 describes the process of PaaS. PaaS vendors also use virtualization technology. Different to IaaS vendors, they also provide a running environment with operation system and other essential middleware. PaaS customers do not need to install the virtual machine and upload the whole virtual machine image. The only thing to upload is the application package or even a configuration file. PaaS vendors may provide some Cloud services such as database service, data storage service, authentication service. The maintenances of the application package retained by customers are in the charge of customers, while the maintenances of the Cloud services and virtual machines are in the charge of PaaS vendors. Because of the providing of standard Cloud services and installed virtual machines, PaaS is less flexible than IaaS.
The service fees are also based on performance usage. A practical example of PaaS products is Google App Engine. [Pij09]
To summarize, “PaaS offerings provide a set of basic services, including virtual servers, storage, and databases. You can use these services to build an application on top of the PaaS platform with the tools, or APIs, provided by the PaaS platform.”[Cha10]
2.2.3 Software as a Service (SaaS)
2 Cloud Computing environment and infrastructures, SaaS vendors also provide already implemented applications as services. SaaS customers neither purchase their own applications or the license nor upload any application package or configuration file. The only thing they need to do is to pay for the SaaS‐fees. Therefore SaaS customers are also the end users. SaaS vendors are in charge of managing the software license, maintaining applications and providing a hosting environment. Another possibility is that SaaS venders could also be the customers of other IaaS or PaaS venders. However, lacking of successful Cloud Computing cases causes most SaaS venders hold the infrastructure and platform, where the applications run. SaaS customers have to accept the standard applications provided by SaaS vendors, which leads to less flexibility. Figure 2.4 describes the implementation of SaaS.
End User
Figure 2.4 Software as a Service
As the infrastructures are transparent to SaaS customers, the service fees are no longer based on performance usage, but “per user per month”. A practical example of SaaS products is IBM LotusLive. [Pij09]
To summarize, SaaS is a kind of “scalable, available, multi‐tenant supported and configurable software deployed as a hosted service and accessed over the Internet.”[Ley09]
2.3 Economics of Cloud Computing
In the last Section we have discussed about three different implementation levels of Cloud Computing. Then we will concern with the choice of three levels of Cloud Computing for enterprise and the Service Level Agreement (SLA) between customer and vendor.
2.3.1 The Alternative of Cloud Computing in Enterprise
In the business economics area, the implementation of Cloud Computing is a kind of Internet‐based IT outsourcing. The requirements of network infrastructures for traditional IT outsourcing are only limited to the capability of guarantee the efficient communication and cooperation between customer and vendor through e.g. email and video conference, which is too far away from the requirements for Internet‐based IT outsourcing – Cloud Computing.
Public Cloud and private Cloud are two kinds of Cloud Computing. The private Cloud is “a marketing term for a proprietary computing architecture that provides hosted services to a limited number of people behind a firewall” [PriCL]. As the private Cloud is built within enterprises, the IT infrastructure for building private Cloud is required. The public Cloud services are provided and delivered through Internet. The enterprises do not need to build, but substitute and receive services. The combination and data exchange between private Cloud and public Cloud could be implemented via VPN. No matter which kind of Cloud services the enterprises prefer, they have to choose a suitable Cloud Computing implementation level. In this paper, we focus on the public Clouds. At the level of IaaS, there is no need to purchase or maintain the IT infrastructure. This part of fixed costs turns to a variable cost, which is used to pay service fees. However, enterprises have to purchase the operation system, application software and their licenses. Additionally, they also have to pay a lot to hunt IT experts, who have to be taken care of in order to prevent the huge lost from their leaving.
At the level of PaaS, enterprises can use some Cloud services like database and operation system provided by service vendors in addition to the IT infrastructures. Compared to the IaaS level, enterprises can save some money for operation system and some general software provided by PaaS vendors. But enterprises still have to purchase some special application software, which are not provided by service vendors. The enterprises have to hunt IT experts as well.
At the level of SaaS, which is the top level of Cloud Computing implementation, SaaS vendors provide a standard solution suit including software, hardware and applications. Enterprises do not need to spend money on any software, hardware or IT experts, as they are the end user to SaaS vendors. The only cost is SaaS‐fee, which is based on “per user per month”. At this level, the IT cost of the enterprise is minimized. Without hardware or software maintenances, the enterprises can totally focus on their key business area.
But at no matter which level of Cloud Computing implementation, the enterprise has to face the risks like the security of business data, the suspension of outsourcing
2 Cloud Computing contract, the bankrupt of the service vendor etc.
2.3.2 Service Level Agreement (SLA)
After the selecting phase of Cloud Computing vendors, the enterprises will sign an outsourcing contract, which contains for example the contract of service, contract of purchase, contract for work and labor etc, with the service vendor. The SLA, which is “a negotiated agreement between two parties where one is the customer and the other is the service provider”, [SLA] plays a significant role in the outsourcing contract.
SLA records the agreements of QoS (Quality of Service), which contain for example performance, availability, storage capacity and reaction time, between both sides. They are measured by numbers such as Time Service Factor (TSF), which is the percentage of the service reaction time within an agreed timeframe, Turn Around Time (TAT), which is the time to accomplish some task.
SLA management is normally divided into two phases: negotiation phase and monitoring phase. In the negotiation phase, the customer and vendor define the concrete service level, while in the monitoring phase the customer monitors the fulfillment of the contract in the runtime. “It is important to note that the “agreement” relates to the services the customer receives, and not how the service provider delivers that service.” [SLA]
2.4 Advantages and Risks
After the introduction of Cloud Computing, let’s turn to the benefits brought from Cloud Computing and the risks, which should be taken care of by vendors and customers.
2.4.1 Advantages
The IT operation cost will be strongly reduced. The capital expenditure turns to operational expenditure, which is better to manage and makes the cash flow more visible. It saves the cost not only for purchase of IT infrastructure, but also for hunting IT experts and training staffs.
With Cloud Computing, the deployment of new applications has been extremely speeded up. As for SaaS, a short time staff’s training of the application is enough, while the in‐house development takes a long development life cycle, which raises the risks and costs.
to solve the technical problem quickly and efficiently. Furthermore, they may have some successful cases to reference and can give a lot of useful suggestions to customers. So the reliability has been improved.
How could the scalability be easily realized by an IT in‐house development enterprise? The enterprise could purchase new hardware or update the available hardware to meet the needs of new requirements. But what would happen if the enterprise finds they do not need so much IT power? They could not just abandon the spare IT resources. Cloud Computing will solve this problem easily. The service fees paid by the enterprise decide the capacity of services received, which makes the dynamically changing of their IT resources possible.
The security, which is most important for enterprise, has been improved by Cloud Computing. Imaging how easily is it to steal a 2kg weighted laptop than an over 10kg weighted server? It is too dangers for an IT expert of an in‐house enterprise to leave his laptop, which may contain a lot of sensitive data, in his car, as there are too many security problems caused by stolen laptops. Even though the enterprise may build a room for their servers, the servers may be touched by some non IT experts. But as for the service provider, the situation is totally different. They provide higher data security to attract new customers via building huge room or even a whole building for their servers, mainframes and super computers. They invest a lot to keep their hardware and software safe, which might be an impossible mission for a middle enterprise.
Besides these advantages, there are still a lot of other benefits brought by Cloud Computing like easier maintenance, metering etc.
2.4.2 Risks
Although the Cloud Computing brings so many advantages, the popularity is still queried by enterprises. Enterprises may have the following trepidations.
Almost all of the enterprises are worried about their sensitive data. They think the data is safe, only if the data is stored within the enterprise and can be touched by them anytime. Just imaging a middle enterprise, which is reasonable to deploy a middle level database to secure and administrate the sensitive data. But how could this middle level database offer a higher level security mechanism as large level databases like Oracle, DB2, which are usually used by service vendors? Enterprises also worry that the service provider might pass their sensitive data to their competitors. In order to solve the problem, private Cloud, which stores enterprises’ sensitive data within enterprises, turns up. Thank private Cloud enterprises not only acquire a higher level of security but also keep their sensitive data under control.
2 Cloud Computing advantages. Those advanced processes may be passed to other competitors by service vendor. Business Process Reengineering (BPR) is one of the solutions for this problem. The enterprise separates those non value added chains and uncritical processes from the whole business process, outsources these separated processes to service vendor, so that they will not give out their competitive advantages. At the mean time, they can also focus on the key fields of business.
As a new solution for enterprise, there are too few successful cases. A stable enterprise may not take this risk. The enterprises may ask, what happens if the service vendor goes bankrupt? Who will be in charge of the contract obligation?
Enterprises also have to consider the cost for the transform from in‐house to outsourcing. In this transform phase, the cost may be huge. The enterprises have to take the risk of not only the corporate culture changing, but also the lost of IT experts or some key persons.
It is also difficult to choose a proper service vendor. A wrong choice may cost a lot. For example, could a service vendor with American corporate culture deliver efficient and reliable services to a German traditional family‐based corporation? Is not the cultural gap between them influence the cooperation? And also enterprises have to consider, where to store their data, in their own country or other countries. What happens if the local law is deferent?
2.5 Component-Based Application Design
The component‐based application design has played a significant role in software engineering area, through which the software development can reduce cost and shorten the development life cycle. “A component framework defines a semi‐complete software architecture that has been carefully parameterized with respect to the components that represent the most variable elements of the domain. A component‐based application can thus be instantiated from the component framework by simply providing the specific components needed for the particular application.” [TVJ+]
There are several different component systems based on various platforms like J2EE and Microsoft .NET, which are the two most popular candidates for Cloud Computing. In SaaS, the services provided by the vendors can be considered as a huge internet‐based application, which contains a lot of component‐based applications. The communication between these applications may be through message mechanism, which is based on Web Services protocols like SOAP, WSDL, and UDDI. When the service vendors establish new service, the new service’s UDDI will be stored in a candidate list. If requestor requires some special service, he will first send the service description to the service discovery facility. After finding out the
favorable service, the requestor will get the service address, which may be described in WSDL. The requestor now can reference the service via service address. The component based application design can make the Cloud Computing to provide scalable services efficiently and accurately.
3 Composite Application Framework
3 Composite Application Framework
3.1 Introduction
The term Composite Application Framework has not been standardized. The enterprise has its own definition for Composite Application. SAP thinks that “Composite Applications are user centric applications supporting highly collaborative and dynamic business processes which span several functional areas across and beyond organizations” [SAP]. Microsoft defines Composite Application as “a collection of software assets that have been assembled to provide a business capability. These assets are artifacts that can be deployed independently, enable composition, and leverage specific platform capabilities” [Bar06].
From the perspective of end‐user, Composite Application is a standalone application. It can be adapted in a relative short time; it does not care of the organization and system boundary but fully utilizes the existing resources; its user interface changes rarely, although the back‐end system has been totally revised. From the technical perspective, the Composite Application is a collection of existing services and components, which aligns existing IT infrastructures with the requirements of end‐user. Furthermore, it realizes loosely coupling between user interface and back‐end system.
3.2 Features of Composite Application Framework
Composite Application Framework has the following features.Heterogeneous services, applications and components should behave as a standalone application in the framework. From the perspective of end‐user, the whole Composite Application acts as a simple and standalone application. There is no need to search a certain application interface to accomplish a certain task. As end‐user’s opinion, the Composite Application might be just a web browser based user interface, which means that the system is transparent to end‐user. This feature is similar to the Cloud Computing introduced in Chapter 2.
The services, applications and components, which compose the Composite Application within the framework, are loosely coupled. When the requirements of enterprise change, the services, applications and components can be easily added, removed or modified with no influence to others. Furthermore, these services, applications, components and computing assets are reusable. The loose coupling leads to the independence between front‐end user interface and back‐end system.
In the framework, the components are capable of communicating with each other. In the Web Services architecture, the communication could be achieved by different Message Exchange Patterns (MEPs), which are explicitly defined in WSDL 2.0 including In‐Only MEP, Robust In‐Only MEP, In‐Out MEP, In‐Optional‐Out MEP, Out‐Only MEP etc.
The framework should support transactional application, which gets data from multiple components and sources.
Besides these features, the framework should provide security mechanisms such as role control and authentication; integrate different applications in a single user interface and provide a uniform Graphical User Interface etc.
3.3 Cafe Project
3.3.1 Introduction
“Cafe (Composite Application Framework) is a methodology, architecture and a set of prototypes that aims at modeling, provisioning and executing composite applications in the Cloud” [Miet]. The project is part of the ongoing PHD work from Ralph Mietzner at University of Stuttgart.
The architecture of Cafe is similar to SaaS application, which has been discussed in the Chapter 2. In the traditional SaaS application, the IT infrastructures and applications are provided by the same application vendor. That is to say, the IaaS, PaaS and SaaS belong to a unique application vendor. Customers can subscribe the standard SaaS application services provided by the application vendor. Generally a standard application cannot satisfy all customers, therefore, the customization has to be issued by costumers. Some customers have its own IT department to handle the customization, while the others choose outsourcing. The deployment by a third IT consulting company is expensive. Customers have to pay the subscription fees as well as deployment fees, which stupendously increase the IT cost. Furthermore, the deployment by the third IT consulting company is risky and requires long deployment life cycle, as the consulting company is neither the application services’ provider nor the receiver of application services.
Cafe architecture raises a new framework to separate the application vendor and the application provider. The Cafe application vendor is in charge of supplying IT infrastructures and standard Cafe application. The application provider purchases the standard Cafe application, whose artifacts are packaged as a Cafe application archive (.car) file, from application vendor. The application provider customizes the
application according to the specified requirements of customers. The services subscribed by a certain customer are totally customized, so that the customer does
3 Composite Application Framework not need to establish his own IT department or ask the third consulting companies to customize the application services. Compare to the traditional SaaS, the customers only need to pay the subscription fees for specific services, which makes the deployment much more quickly. As for the redeveloper of application services so‐called application provider, the development life‐cycle of customization is relative short. The application provider could improve his application by learning from the customer’s requirements, and turns these improvements to his competitive advantages.
Figure 3.2 describes the implementation of from service vendor to service provider delivered application service example. The GUI Component acts as a user interface and runs above the JBOSS App Server. The Component can be accessed by user via URL, while the Workflow Component provides EPR address for invoking specified business process and returns the result back. Finally, the data generated by Workflow Component presents on the GUI Component. Figure 3.1 simplifies the diagram by using Compartment’s Collapsible attribute.
The task of this paper is to describe how to develop the graphical editor, which supports the easily drawing of Figure 3.1 and Figure 3.2, generates the Cafe application descriptor with Eclipse Graphical Modeling Framework (GMF), and exports the corresponding .car file by Eclipse Plug‐In Development Environment.
Figure 3.1 Collapsed Example of Cafe Application
Figure 3.2 Extended Example of Cafe Application
3.3.2 Editor for Application Vendor
In Figure 3.3 displayed Ecore diagram shows us the meta‐model of the editor components.
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Component is an important part of the diagram. There are three different Component Patterns, Single Instance, Single Configurable Instance and Multiple Instances, which are distinguished by different icons in the diagram and displayed in Figure 3.5.
Figure 3.5 Component Patterns
For different customers, parts of their requirements are identical. For example, almost every international commercial company needs the direct quotation of exchange rate. This kind of Component can be set as a Single Instance Component, which provides the same information to all customers. It does not need to know which subscriber is invoking. Therefore no specific configuration is needed. The provider needs to deploy it only once. The update can be applied to all customers, who subscribe this Component service. Furthermore, the same Single Instance Component can be deployed multiple times. The subscription and invoking is controlled by load balancer proportionately.
If customers need the specific subscription, the application provider should provide the customer specific Component, which is supported by Single Configurable Instance Component. The Component is aware of every subscriber and provides configured services. For example, the service fees calculation Component sends customer specific invoice monthly according to the contract. Generally, the Single Configurable Instance Component needs to be deployed only once. Adding new subscription does not cause the redeployment, while the updating causes the redeployment. The same as Single Instance Component, one Single Configurable Instance Component can be deployed multiple times. The subscription is handled by load balancer as well.
Sometimes the provider needs to change the Single Instance Component to Single Configurable Instance Component, which results in the redesign of the Component and the reboot of the system. To reduce the cost and increase the availability, Multiple Instances Component turns up. The specific instance is deployed to each customer, so that there is no influence to the other running Components by adding new Component. As the relationship between instance and customer is one to one, the load balancer is no more necessary.
The running of some Components depends on the environment provided by other Components. In order to express this kind of dependence, Deployment Relation is
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3 Composite Application Framework
The last component in the diagram is Variability. It acts as the source of Component Dependency, which describes the relationship between Components and has been displayed in Figure 3.4.
3.3.3 CAR: Cafe Archive File
The diagram together with the generated XML description file and the files appeared in Implementation attributes should be packaged as a .car file, which acts as a
configuration file sent from application vendor to application provider. The implementation of generating .car file is through the extension of Export Wizard
Extension Point in Eclipse Plug‐In Development Environment, which will be introduced in details in Chapter 5.
4 Eclipse Modeling Projects and Plug-In
4.1 Introduction and Background
4.1.1 Eclipse
The original meaning of Eclipse is “an astronomical event that occurs when one celestial object moves into the shadow of another.” [Ecl]. When IBM chose “Eclipse” to name its new Java Integrated Development Environment (IDE), it was directly targeting the Microsoft’s Visual Studio and Sun Microsystems’ Sun One Studio. After a nine‐year development, Eclipse became one of the most popular IDEs in the Open Source Community not only for Java but also for C, PHP and other programming languages.
According to the official definition, “Eclipse is an open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle.” [Ecli]
4.1.2 Model-Driven Software Development (MDSD)
Generally, talking about the modeling diagram, the UML (Unified Modeling Language) and the diagrams drawn with UML come into our mind. A lot of development teams have increased productivity and quality by introducing the Model‐Driven Software Development.
Before using the Model‐Driven Development (MDD), a Model‐Driven Architecture (MDA), which is “a software design approach for the development of software systems” [MDA], has to be built firstly. The MDA includes defining Platform Independent Model (PIM), determining the target platform, defining the transformation and applying the transformation either manually or automatically. Thank MDD, software development now turns to a model transformation. All of the models are independent with each other and separately defined. Each transformation is from an abstract level to a less abstract or concrete level, until a target system implementation is reached. The EMF (Eclipse Modeling Framework) and GMF (Graphical Modeling Framework), which will be introduced later, are the implementations of OMG modeling standards. Therefore, the development of the graphical editor with GMF is based on MDSD.
4 Eclipse Modeling Projects and Plug‐In
4.1.3 The Eclipse Modeling Project
Eclipse Modeling Project, which is a relative newer top‐level project in the Eclipse Community, aims to improve and widespread MDSD technology within the Eclipse Community. It provides the following capabilities: Abstract Syntax Development, Concrete Syntax Development, Model Transformation and the latest started Modeling Amalgamation Project (Amalgam), which “provides improved packaging, integration, and usability of Modeling project components” [EclMP].
Abstract Syntax Development includes the core project of Eclipse Modeling Project – Eclipse Modeling Framework (EMF), which has been existed since the appearance of Eclipse platform. EMF provides Model Transaction component, Model Validation framework, Model Query component and Model Search component etc. It also “supports the definition of abstract syntax for modeling languages like Object Constraint Language (OCL) and Unified Modeling Language (UML)” [EclMPC].
Within Concrete Syntax Development it contains Graphical Modeling Framework (GMF) “providing a generative component and runtime infrastructure for developing graphical editors based on EMF and GEF” [EclMP] and Textual Modeling Framework (TMF) “providing tools and frameworks for developing textual syntaxes and corresponding editors based on EMF” [EclMP]. With GMF we can generate a powerful graphical editor, while with TMF we can create a high quality textual editor. In this paper we focus on the GMF.
Using Model‐to‐Model Transformation (M2M) and Model‐to‐Text Transformation (M2T) projects we can generate a user‐defined graphical or textual editing environment. Within the M2M project the M2M rules can be defined to generate another model from already existed instance models, while within the M2T project the M2T rules can be defined to generate the requested text template.
4.2 Eclipse Modeling Framework (EMF)
“The EMF project is a modeling framework and code generation facility for building tools and other applications based on a structured data model” [EMF]. It helps programmer to generate Java code from user‐defined models automatically. The generated Java code can be modified and edited just like other normal Java code. For example, the user‐defined methods and variables can be added. When the Java code has to be regenerated caused by model changing, the user‐defined methods and variables will not be overwritten using Java annotations. The model can be stored as an XML file, which has been widely used as a standard, so that the capability of model interchange is quite easy. On the contrary, the model can be created by annotated Java code or XML.
decorator model for the Ecore Model” [EMFfaq], is used to define or control the generation process. EMF provides the following key functions: EMF (Core), Compare, Model Query and Validation Framework.
4.2.1 EMF (Core)
EMF contains the following three fundamental parts: EMF, EMF.Edit and EMF.Codegen. Within the core EMF framework, Ecore is used as a meta‐model to describe model and the runtime environment. The details and the creation of Ecore will be discussed in Chapter 5.
EMF.Edit framework provides an easy understanding graphical editor, where the model is modified. In the meantime, the stored XML file is also modified synchronously. Using command stack makes the editor to support the automatic undo and redo.
EMF.Codegen facility is able to generate the Java code to build the EMF model editor.
4.2.2 Compare
EMF Compare “brings model comparison to the EMF framework, this tool provides generic support for any kind of meta‐model in order to compare and merge models” [EMF] Moreover, it also provides the following different compare methods: a Standalone Core providing a jar‐based comparison independent of Eclipse runtime, Team Providers Integration with SVN, CVS or GIT, Extensible Framework developed by Eclipse Plug‐in facility.
4.2.3 Model Query
The query component “facilitates the process of search and retrieval of model elements of interest in a flexible yet controlled and structured manner” [EMF]. Model Query provides the SQL‐like query methods. The SELECT class accesses the
set of models iteratively, collects the result set according to the query conditions to
QueryResultSet object and then returns the QueryResultSet to the caller. The FROM class determines or limits the search area and provides an iterator for
elements in the search area. The WHERE class restricts the query conditions. The UPDATE class is similar to the SELECT class, and additionally provides the
modification function. QueryResultSet class is used to store the result sets and
return them to the caller. Moreover, Model Query provides EObjectCondition
class, ConditionPolicy class and
4 Eclipse Modeling Projects and Plug‐In
4.2.4 Validation Framework
Validation Framework provides batch and live validating methods. The validation process can be either explicitly executed after the modification of models or implicitly and live invoked during the modifying of models. The implicit validation needs a validation listener to monitor the validation events. Within the Validation Framework, the programmer can define various constraints with either Java or OCL.
4.3 Graphic Editing Framework (GEF)
4.3.1 Introduction
After creating the meta‐model through EMF and generating our user‐defined model, a graphical editing environment is needed to simplify the model development. A general problem is how to reflect the modification in graphical editor to the model description file synchronously. For example, when editing the graphical description of BPMN in a graphical editor, the corresponding XML schema should also be changed synchronously. Model‐View‐Controller (MVC) is one of the most popular solutions used in GEF.
“The Graphical Editing Framework (GEF) allows developers to create a rich graphical editor from an existing application model. It consists of 2 Plug‐ins. The org.eclipse.draw2d plug‐in provides a layout and rendering toolkit for displaying graphics. GEF employs an MVC architecture which enables simple changes to be applied to the model from the view” [GEFWiki].
4.3.2 Model-View-Controller (MVC)
Model‐View‐Controller (MVC) is “a software architecture, currently considered an architectural pattern used in software engineering. The pattern isolates domain logic (the application logic for the user) from input and presentation (GUI), permitting independent development, testing and maintenance of each” [MVC]. In MVC architecture, Model acts as back‐end, which provides the operation of application, the generated front‐end View is generally represented by a GUI, which presents the back‐end Model with various graphics or other ways. The Controller accepts the input from Viewer; passes it to the back‐end model and then returns the results to Viewer.
The following description is about the MVC control flow. The user changes the Viewer in UI through e.g. mouse click. The Controller listens the UI event and handles the input event. After converting the event to a Model understandable access, the Controller passes the converted event to back‐end Model. The Model will
do some corresponding operations and notify the Viewer through Controller. The modification will be represented in the UI. Through the decoupling of Model and View, which increases the reusability of code, the complexity of Model and View design has been reduced.
4.3.3 Draw2D
Within the GEF editor, the elements like figure, text, layout and connection drawn by user are provided by org.eclipse.draw2d plug‐in package.
Before painting figure, the paint() method will do some initializations like
preparing the font, foreground and background color. After the initialization, the
paintFigure() method is called to paint figures. In case the child figures are
needed, the paintClientArea() method, which sets up a specified area for child
figures, has to be invoked. Any operation on child figures is not allowed to beyond this area. After setting up the specified area, the paintChildren() method is
invoked to paint child figures. Finally, the paintBorder() method is called to
specify the border of the figures. The child figure is not allowed to exceed its parent’s border. Otherwise, the exceeded parts have to be cut off. During the painting, we can use org.eclipse.draw2d.label and org.eclipse.draw2d.text package to add label or text.
After painting the figures, the layout setting is checked. If layout is used, the implementation of layout is divided into two steps. Firstly, all figures will be marked as “invalid”. Secondly all these marked figures will be validated. During the validation, the information like minimum, maximum and preferred size, position etc. has to be proved. If the figure is modified, these two steps of validation have to be reprocessed.
Draw2d also provides connection figure, which is a special figure. Connection figure aims to connect other figures from various child areas. Therefore, the border of connection figure is not defined. 4.3.4 GEF In MVC architecture, draw2d provides View with figures and connections while the Ecore in EMF provides the meta‐model for different GEF models. These models can be written in various formats like Java code, XML Schema. The Controller function is provided by GEF EditPart, which provides a bridge between View and Model. It converts user interacted events in UI to model understandable commands and then sends them to model, so that the model modifications can be implemented according to the UI events. And vise vase, the modifications in Model can be reflected to the UI Viewer.
4 Eclipse Modeling Projects and Plug‐In Converting the model to our user‐defined view is relative simple. It is usually realized by adding listeners, which invoke the refresh operation on the view. But converting the UI events to model is much more complex. As soon as the modifications take effect, a request is generated to require the interface and commands, which are in charge of the modifications, in the model. At the same time the edit policies are set. The detailed interaction of this process is beyond this paper. We will not expend it here.
4.4 Graphic Modeling Framework (GMF)
4.4.1 Introduction
Compared with GEF project, GMF project is fresher and “provides a generative component and runtime infrastructure for developing graphical editors based on EMF and GEF. It aims to provide these components, in addition to exemplary tools for select domain models which illustrate its capabilities” [GMF]. GMF is based on MVC architecture and separates the diagram and domain model, which increases the productivity and quality.
During GMF development, programmer uses Ecore to describe meta‐model. According to the description in Ecore, the model, edit, editor and tests codes are automatically generated by EMF Generator Model. In addition, GMF UI also extends the org.eclipse.draw2d package.
4.4.2 Graphical Modeling Framework Tooling
“The GMF Tooling consists of editors to create/edit models describing the notational, semantic and tooling aspects of a graphical editor as well as a generator to produce the implementation of graphical editors” [Pla06].
After generating the model, edit and editor codes, the Graphical Definition Model, which contains the root element canvas, can be created. There are five kinds of element in canvas, which are Figure Gallery, Node, Diagram Link, Compartment and Diagram Label. Each Figure Gallery has several Figure Descriptors. Under Figure Descriptor one kind of Figure Shapes, e.g. rectangle, rounded rectangle, ellipse, polyline, template point, polyline connection and custom figures etc., can be added. Dimension, layout, label, border and color are stored as shape’s attributes, which can be setup separately. Finishing the setting of Figure Gallery, the Node element can be added and references the corresponding Figure Descriptor. If the label attribute has been set in the Figure Shape, a Diagram Label element need to be added and linked with it. The Diagram Link is used to associate with the connection figure in the Figure Descriptor,
while the Compartment is usually contained within other figure.
After the editing for Graphical Definition Model, the Tooling Definition Model, which is relative simple, need to be created. It defines the elements, the name of elements, and the icon of elements in editor palette. The order of elements in Tooling Definition Model determines the order of the elements in palette.
The fundamental working stage is accomplished now. Next step is to create a Mapping Model, which is the heart of GMF models and represents a diagram. In the Mapping Model there are Canvas Mapping, Top Node Reference and Link Mapping.
Canvas Mapping defines the domain model, element, palette, diagram canvas etc. which link the already generated Ecore Model, Graphical Definition Model and Tooling Definition Model.
Top Node Reference indicates the figures, which can be directly displayed on the diagram surface. It links Diagram Node and Tool through its Node Mapping child element. If there is any child figure so‐called compartment within it, a Child Reference is needed, and the Compartment Mapping is used to map the corresponding Compartment in the Graphical Definition Model. Moreover, the Constraint, which is written in Object Constraint Language (OCL) or Java, can be defined. Its tasks include element initialization, link constraint, audits etc.
As for the Connection figure, a Link Mapping is specified to build the relationship between Diagram Link and Tool. The source and target have to be set explicitly.
The Generator Model, which provides the largest model in GMF, is generated based on the Mapping Model and Ecore Model.
4.4.3 Graphical Modeling Framework Runtime
“The generated plug‐in depends on the GMF Runtime component to produce a world class extensible graphical editor” [Pla06]. GMF runtime provides a set of reusable components such as toolbar, palette, diagram menu, connection handles, pup‐up bars, outline view, diagram export to image files etc. It also supports the bridging of EMF and GEF. The service provider infrastructure and extensibility options provide the interface to develop new runtime components based on Eclipse Plug‐In Development Environment via ExtensionPoints. Details of GMF runtime components will be introduced with examples in Chapter 5.
4.4.4 Beyond GEF and EMF
GMF is not only the name combination of GEF and EMF, but also a functional combination of both, which provides higher extensibility to meet the special needs
4 Eclipse Modeling Projects and Plug‐In of development. Just imaging a complete graphical editor is like a comfortable room for your study. The model built with EMF is a basic renting apartment without any furniture. The graphical editor implemented by GEF is the furniture you have bought. The various fees such as water costs and energy costs you have to pay are the maintenances of the editor. But when you use GMF, congratulations! You just rent a student dormitory, which has some furniture for your comfortable study. You do not need to pay other costs but the rent. If you think the furniture is not your taste, you can even buy anything as your will. Compared to GEF and EMF, GMF not only saves a lot of developing costs, but also provides the flexible Plug‐In mechanism.
4.5 Plug-In Development Environment (PDE)
Eclipse is a grown and extensible architecture, which provides an open source platform for creating an extensible IDE. One of the principles of Eclipse platform is the seamless integration of plug‐ins with the workbench and other plug‐ins. The whole Eclipse IDE is an aggregation of various plug‐ins with a runtime core.
In the whole Eclipse plug‐in development environment, extension point, which provides the interface for plug‐ins, is a very important and useful concept. Every plug‐in is developed based on the existing extension point. Those user‐developed plug‐ins can also provide their extension points, so that the further development based on them is possible. Among all of the plug‐ins, Workbench and Workspace are two obligated plug‐ins, which provide a lot of extension points.
Thank plug‐in concept, the launch of Eclipse IDE is much simpler. The core of the platform starts first, and then the system plug‐ins will be found and loaded. Most of the Eclipse’s functions are implemented by plug‐ins. For example, the Workbench UI plug‐in realizes the viewer of Eclipse IDE, which provides extension points for creating plug‐ins to change file menu or add tooling buttons. Even the Java Development Tooling (JDT) is one of the Eclipse’s plug‐ins.
Theoretically speaking, Eclipse IDE is a big puzzle. Everyone can add or remove plug‐ins to build the most suitable Eclipse IDE. The detailed introduction of Eclipse Plug‐in Development Environment is beyond this paper. In Chapter 5 we will give out some closing introductions through the development of car file export plug‐in.
5 Implementation of Graphical Editor
5.1 Installation of GMF
Eclipse community provides three ways to get GMF plug‐in. The first way is using Eclipse Software Update Manager to download and install the plug‐in automatically. After the installation, the Eclipse has to restart to take the plug‐in into effect. The second way is going to the GMF download site to download the plug‐in package, manually copy the plug‐in folder into Eclipse plugins folder. Starting the Eclipse,
you will find the GMF plug‐in has been installed and is ready to use. The third way is the simplest way. You can directly go to the Eclipse download site and choose the Eclipse Modeling Tools, which collects almost all of the Modeling Project components like EMF, GMF etc. In this paper I have downloaded Eclipse Modeling Tools directly.
After downloading and starting Eclipse, the Workspace should be set. Then we can use Eclipse New Wizard to create a new GMF Project, which is displayed in Figure 5.1.
5 Implementation of Graphical Editor After creating the new GMF Project, the project folder structure in Eclipse Package Explorer should be seen as the Figure 5.2.
Figure 5.2 Project Folder Structure
The first step for GMF project development is to create Ecore Model via Eclipse New Wizard, which is the meta‐model for the later generated models. The Java codes generated based on Ecore model are the implementation of EMF, which provides the fundament for GMF development. After generating EMF Java codes, the development of EMF is accomplished. GMF implementation starts with establishing Graphical Definition Model, Tooling Definition Model and Mapping Model through Eclipse New Wizard. These models support the Generator Model, which generates the diagram codes. In the following Sections, we will introduce the whole Cafe application editor implementation process in details.
5.2 Ecore Model
5.2.1 Introduction
Ecore is a kind of meta‐model used to describe EMF model. Ecore model is also a kind of EMF model, so at the same time, Ecore model is also a meta‐meta‐model. In Ecore model there are following components: EPackage, EClass, EAttribute, EReference, EEnum and EDataType etc.
EPackage is the root of Ecore model, which defines the namespace. EClass
represents a class, which contains an arbitrary amount of EAttributes and EOperations. ERefference describes the connection and relationship between
two EClasses. EEnum is an enumeration type, in which exists at least one EEnumLiteral. EDataType indicates the type of EAttribute like string, int, float etc.
EMF provides a graphical editor for the constitution of Ecore model, which can be implemented as simple as drawing UML diagram by drag and drop. The XML file describing the Ecore model changes automatically according to the modification of Ecore diagram. The Ecore model constitution process will be introduced upon the requirements of Cafe application in next Section.
5.2.2 Ecore Model Constitution
First let’s look at the constituted Ecore model diagram and the diagram editor in Figure 5.3.
Figure 5.3 Ecore Model Diagram and Diagram Editor
In the left zone of the picture is a tooling palette. Developer can choose the appropriate objects or connections, and then put it in the canvas through drag and drop. The bottom zone shows the property of canvas and canvas components. The value of property can be input. For example the Name, Ns Prefix and Ns URI of
Epackage are set as cafeApplication. The Ecore diagram is constituted
