Requirement engineering (RE) explores the objectives of various stakeholders and the activities carried out by the system. In regard to system objectives and system functionalities, in this chapter we examined one of the existing ap- proaches — specifically the goal-oriented approach as illustrated in Dardenne et al. (1993). Generally, goal-oriented approaches until now have been mainly directed to assist in the development of software systems, as opposed to focussing on document warehouses involving XML-embedded structures. Based on this, we obtained and broadened the notion of this goal-modelling approach to XML document warehouses (XDW) to promote their structural design by identifying the data warehouse dimensions and the nature of the fact repository. We introduced concepts from our previous work (Nassis et al., 2004, 2005a, 2005b), where we presented a coherent way to integrate a conceptual design methodology to build a native XDW, which includes the XML FACT (xFACT) repository and the Virtual Dimensions (VDims). At this stage we concentrated only on the aspect of the data warehouse structure and design. Given the architecture of the XDW which consists of three levels: (1) Requirement level, (2) XML warehouse conceptual level and (3) Logical level, we focus on the first level by proposing the XDW requirement model.
The main themes of our methodology are to: (1) capture requirements early in the design process; (2) understand the current requirements and further elicit these to promote new requirements; (3) illustrate the mapping of each stated requirement into a corresponding dimension of the XML document warehouse
(XDW); (4) certify that the information required for the xFACT repository can be assembled from the information available in the XDW; and (5) ensure that the information necessary to construct a dimension is available or can be obtained from the xFACT repository.
We identified the main characteristics comprising the requirement model and then proceeded to the precise and detailed terminology of the components. Using as a basis the system context of our case study (Conference Publications), we extracted a number of sample requirements and applied these to our XDW requirement model in order to illustrate the concepts presented throughout. In the chapter we emphasized the importance of requirement validation and the availability of the necessary data that aid to requirement fulfilment. A significant issue that still needs to be addressed is checking for the consistency of requirements. This can be achieved by adding an enhanced annotation that will promote a basis for verifying requirement consistency. This process involves two major factors: (a) ensuring that the requirement presentation has sufficient annotation to capture all the constraints in a precise manner, and (b) the development of an algorithm that is capable of carrying out such consistency verification, specifically dealing with inheritance and recursion. One avenue that could be pursued is the use of a language such as Object Constraint Language (OCL) to annotate the requirements.
Clearly, there are several more subject matters that deserve investigation. First, the development of formal semantics that automate the mapping between XML data and XDW schema will define views more precisely and hence support the incremental update of materialized views. Nowadays, the major challenge for any level of semi-structured data is its ability to be effectively searched. Given that the amount of content expands across an organization, locating specific resources becomes progressively more complex and time-consuming. There- fore, investigating performance issues upon query execution in relation to accessing the XDW will prove valuable. A significant aspect is the implemen- tation of the XDW requirement modelling approach, which can be achieved by building a well-formulated empirical study. Also to be explored is the construc- tion of a critical case study to evaluate and validate the application of the XDW requirement model for XML document warehouses (XDWs).
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