Implementing Geographic Information System Grid Services Using Distributed Messaging Systems

Implementing Geographic

Information System Grid

Services Using Distributed

Messaging Systems

Marlon Pierce

SERVOGrid Basics

n SERVOGrid is our project to build a distributed computing

infrastructure to support earthquake simulation codes.

n Distributed Computing Infrastructure

• Services for remotely executing applications, managing distributed files in

logical units, monitoring applications, archiving user projects, and so on.

• Variously called “Grids” (DOE), “Cyberinfrastructure” (NSF), “

e-Science” (UK e-Science program), ….

n The above is sometimes referred to as an “Execution Grid”.

• We designed this around a web service architecture. • See links at the end for more information.

n But what about the data?

• Need ways to access remote data sources through programming

interfaces.

• Practice often is to download (via FTP) entire catalogs and hand edit to

get data you want in the format you want.

SERVO Apps and Their Data

n Disloc: handles multiple arbitrarily dipping dislocations (faults)

in an elastic half-space.

• Relies upon geometric fault models.

n GeoFEST: Three-dimensional viscoelastic finite element model

for calculating nodal displacements and tractions. Allows for realistic fault geometry and characteristics, material properties, and body forces.

• Relies upon fault models with geometric and material properties.

n Virtual California: Program to simulate interactions between

vertical strike-slip faults using an elastic layer over a viscoelastic half-space.

• Relies upon fault and fault friction models.

n RDAHMM: Time series analysis program based on Hidden

Markov Modeling. Produces feature vectors and probabilities for transitioning from one class to another.

Where Is the Data?

n QuakeTables Fault Database

• SERVO’s fault repository for California.

• Compatible with GeoFEST, Disloc, and VirtualCalifornia • http://infogroup.usc.edu:8080/public.html

n GPS Data sources and formats (RDAHMM and others).

• JPL: ftp://sideshow.jpl.nasa.gov/pub/mbh • SOPAC: ftp://garner.ucsd.edu/pub/timeseries

• USGS: http://pasadena.wr.usgs.gov/scign/Analysis/plotdata/

n Seismic Event Data (RDAHMM and others)

• SCSN: http://www.scec.org/ftp/catalogs/SCSN

• SCEDC: http://www.scecd.scec.org/ftp/catalogs/SCEC_DC • Dinger-Shearer: http://www.

scecdc.org/ftp/catalogs/dinger-shearer/dinger-shearer.catalog

What Are Web Services?

doing distributed computing with XML.

• WSDL: Defines interfaces to functions of remote components. This is the programming interface.

• SOAP: Defines the message format that you exchange between components. This carries the messages over the network.

• Web Services are not web pages, CGI, servlets, applets.

n XML provides cross-language support n Suitable for both human and

application clients.

n We built SERVOGrid’s execution grid

services this way.

n We are building data grid components

in the same fashion.

• Allows us to build general purpose client environments like Web portals

User Interface Server

DB Service 1

JDBC DB Job Sub/Mon And File Services Operating and Queuing Systems WSD L WSDL Browser Interface WS DL WSD L WS DL WS

DL WSDL

Viz Service WSDL

Host 1 Host 2 Host 3

IDL GMT

SOAP SOAP

GIS Standards for Data Grids

n

Geographic Information Systems

• ESRI: commercial company with many popular GIS

products.

• Open Geospatial Consortium (formerly OpenGIS

Consortium).

• We will focus on OGC since they define open and

interoperable standards.

n

What are the characteristics of a GIS system?

• Need data models to represent information • Need services for remotely accessing data.

Open GIS Services

n GML abstract data models can encode data but you need

services to interact with the remote data.

n Some example OGC services include

• Web Feature Service: for retrieving GML encode features, like faults,

roads, county boundaries, GPS station locations,….

• Web Map Service: for creating maps out of Web Features

• Sensor Grid Services: for working with streaming, time-stamped data.

n Problems with OGC services

• Not (yet) Web Service compliant

n “Pre” web service, no SOAP or WSDL

n Use instead HTTP GET/POST conventions.

• Often define general Web Service services as specialized standards

n Information services

GML: A Data Model For GIS

n

GML 3.x is a interconnected suite of over 20 connected

XML schemas.

n

GML is an abstract model for geography.

n

With GML, you can encode

• Features: abstract representations of map entities.

• Geometry: encode abstractly how to represent a feature

pictorially.

• Coordinate reference systems

• Topology

• Time, units of measure

Example Use of GML

n The SCIGN (Southern

California Integrated GPS Network) maintains online catalogs of GPS stations.

n Collective data for each site is

made available through online catalogs.

• Using various text formats.

n This is not suitable for

processing, but GML is.

n GML can be used to describe

GPS using Feature.xsd

schema, with values encoded at GPS observations.

Anatomy of WFS (G. Aydin)

n WFS provides three major services as described in OGC specification:

• GetCapabilities: The clients (WMS servers or users) starts with requesting a

document from WFS which describes it’s abilities. When a getCapabilities request arrives, the server dynamically creates a capabilities document and returns this.

• This is OGC’s formalization of metadata, so important to GEON, ESG, etc.

• DescribeFeatureType: After the client receives the capabilities document he/she

can request a more detailed description for any of the features listed in the WFS capabilities document.

• The WFS returns an XML schema that describes the requested feature. • Metadata about a specific entry.

• GetFeature: The client can ask the WFS to return a particular portion of any

feature data.

• GetFeature requests contain some property names of the feature and a Filter

element to describe the query.

• The WFS extracts the query and bounding box from the filter and queries the

feature databases.

• The results obtained from the DB query are converted the feature’s GML

Example WFS Capability Entries

Text block describing any access constraints imposed by the service provider on the WFS or data retrieved from that service. The keyword NONE is reserved to indicate no access constraints are imposed.

AccessConstraints

Contains a text block indicating any fees imposed by the service provider for usage of the service or for data retrieved from the WFS. The keyword NONE is reserved to mean no fees.

Fees

Defines the top-level HTTP URL of this service. Typically the URL of a "home page" for the service.

OnlineResource

Contains short words to aid catalog searching.

Keyword

Descriptive narrative for more information about the server.

Abstract

Human-readable title to briefly identify this server in menus.

Title

A name the service provider assigns to the web feature service instance.

Name

Sample Feature- CA Fault Lines

<gml:featureMember> <fault>

<name>Northridge2</name>

<segment>Northridge2</segment> <author>Wald D. J.</author>

<gml:lineStringProperty> <gml:LineString srsName="null"> <gml:coordinates -118.72,34.243 -118.591,34.17 </gml:coordinates> </gml:LineString> </gml:lineStringProperty> </fault> </gml:featureMember>

n After receiving getFeature

request, WFS decodes this request, creates a DB query from it and queries the

database.

n WFS then retrieves the

features from the database and converts them into GML documents.

n Each feature instance is

wrapped as a

gml:featureMember element.

n WFS returns a

wfs:FeatureCollection

•A WFS can serve multiple feature types data.

•WFS returns the results of GetFeature requests as GML documents (Feature Collections). •Clients may include other

Conclusion and Other Topics

n

We have reviewed Community Grids Lab efforts to

build a GIS-compatible set of data grid services.

• This provides a unified architecture for grid execution and

data grid services.

n

Two other important topics:

• Managing messaging between components.

n NaradaBrokering project led by Dr. Shrideep Pallickara.

n www.naradabrokering.org

• Managing client environments

n Component-based portals: www.collab-ogce.org.

n Command line and scripting interfaces for web services:

More Information

n My email:

• [email protected]

n Overview (submitted to ACES special issue of PAGEOPH).

• http://www.servogrid.org/slide/GEM/SERVO/ISERVO_ACES_PAGEOPH.doc

n QuakeSim Project Page:

• http://quakesim.jpl.nasa.gov/

n QuakeSim Portal:

• http://www.complexity.ucs.indiana.edu:8282.

n QuakeTables Fault Database:

• http://infogroup.usc.edu:8080/public.html

n Community Grids Lab GIS Grid Development:

• http://www.crisisgrid.org/.