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For Topical Session 47 at the 2003 GSA Technical meeting.

Web Services and Geologic Data Interchange

SimonCox

Keywords: data transfer, world wide web, web services, XML

Web-hosted Spatial Data Infrastructures are being developed in many jurisdictions. With the emergence of standardised data encodings, in particular using XML, interest has shifted from catalogues to web interfaces directly to data. The Open GIS Consortium (OGC) is designing interfaces in the form of standardised syntax for operations composed as request-response message-pairs carried over http. Published specifications include Web Map Service (WMS) which concerns maps transported as digital images, Web Feature Service (WFS) which provides access to geographic objects and their properties, and Geography Markup Language (GML) which provides XML components and a basic data model to encode descriptions of geographic objects. Under the Sensor Web Enablement initiative the same pattern is used for interfaces to dynamic sources, such as sensors and simulators.

The OGC Web Service interface (OWS) specifications define services in terms of their public interface, and do not prescribe the internal structure of either server or client software. Implementations, therefore, are usually in the form of facades on top of existing data services such as GIS and RDBMS on the server side, and as additional import options in desktop map-viewers on the client side.

Because of the focus on the public interface between software, interoperability within a specific application domain, such as geology, is enabled by standardisation of the encoding of the response payload. Optimum behaviour requires agreement not only at the level of the low-level syntax (XML, GML Feature-property model) but also in the detailed information models that are being serialised (e.g. a common model and encoding for boreholes, or for mineral deposits). The community language is defined as a GML application schema. The intention is that many servers with differing private data models (e.g. RDBMS schemata) and different persistence mechanisms (e.g. RDBMS vs. OO-DB vs. XML-DB) can all serve geologic information according to the same data model serialised in a common way. In this context different sources can be used according to the usefulness of the data, rather than the technology used by the host organisation.

XMML A standards conformant XML language for geology features

SimonCox

Keywords: data models, XML, UML, standards, information communities

In order to engage in a productive discourse a community must adopt shared definitions for the items of interest to that community. When the information items are imported and exported from automated processing software, then the models and serialised instances must be expressed rigorously and precisely. Many notations are available. Of particular interest are the object-oriented Unified Modelling Language (UML), and the eXtensible Markup Language (XML) with its associated schema languages, especially the W3C XML Schema Language (XSD). Some features of XSD (type derivation, element substitutability) are closely related to object-modelling capabilities (inheritance, polymorphism), so it is possible to use XSD directly as a conceptual schema language. Conversely, XML can be used to instantiate objects defined by UML classes.

Standard web-service interfaces to geospatial information have been developed by the Open GIS Consortium (OGC). Geography Markup Language (GML) is a key element in these interfaces, acting as the basis for XML serialisation of data payloads. However, GML is a meta-language, providing components and a basic data model for use in community-specific application languages. In order to take advantage of OGC Web Service interfaces, therefore, a community such as geoscience must express its data model as a GML Application Language.

We have been developing the eXploration and Mining Markup Language (XMML) in this vein. XML technology lends itself to modularisation, so XMML is being developed progressively, according to the needs of project sponsors. These include geological surveys and mines departments, mining and exploration companies and service providers, and R&D organisations. XMML is being deployed for interprocess-communication, inter-organisational data transfer, and archiving. Many of the components are relevant to generic geology and geophysics, and are not solely artefacts of mineral exploration.

In developing XMML we are using both XSD and UML for design and documentation. GML uses a particular style of XML, which requires that the UML must also follow certain idioms, particularly concerning associations. However, providing that these rules are followed, it is relatively straightforward to incorporate additional components for which UML models are available into XMML.

Developing a generic Geoscience Markup Language: GeoSciML

TimDuffy, MarcusSen, JamesPassmore, British Geological Survey.

Keywords: data transfer, standards, geoscience information, XML, world wide web, GeoSciML

The British Geological Survey (BGS) has been collecting geoscience data since it was founded in 1835, and is the UK national centre for earth sciences covering all the major disciplines within geology and geophysics. It operates both in the UK and internationally . A major role of the BGS is one of data custodian, and in recent years has put major effort into making this data more accessible both to internal and external users, and a key component to this is the use of web technologies including XML for data transfer.

It is possible for an organization simply to design an XML schema for a particular problem at hand and make it generally available. Though not ideal, this is an improvement on having many varieties of non XML data formats. This is because the XML format is partially self-documenting and provides common methods for parsing files, obtaining their structure and transforming them to alternative formats. If communities share a common data transfer model for their domains of interest, data exchange becomes even easier.

Initial work at BGS with XML was based on in-house DTDs for particular applications. Having gained experience with these we believe it is important for further work to develop some common ML for exchange of generic geoscience information. This is not being done from scratch, but as an application of the OpenGIS consortium's (OGC) Geography Markup Language (GML) and building upon the applied geoscience domain focussed eXploration and Mining Markup Language (XMML), by using XML Schema modularity capabilities. These are both fairly complex specifications and this paper describes our experiences in developing from them in an incremental and piece-wise manner to cover some particular geoscientific domains of interest all within one overarching GeoSciML schema. With the support of suitable software tools the model development can proceed in an iterative manner with rapid prototyping incorporating potential domain users feedback. We propose that a similar development process be extended to the wider geoscience community, with the support of bodies such as the International Union of Geological Sciences' (IUGS) Commission for the Management and Application of Geoscience Information and the OGC, so that GeoSciML can become a common language for generic geoscience information exchange using XML based web processes.

-- MarcusSen - 15 Jul 2003

Submission details

-- SimonCox - 12 Jul 2003
Topic attachments
I Attachment Action Size Date Who Comment
WebServices.PPTPPT WebServices.PPT manage 237.0 K 06 Feb 2004 - 17:51 SimonCox Web Services presentation
XMML.PPTPPT XMML.PPT manage 304.0 K 06 Feb 2004 - 17:50 SimonCox XMML presentation
Topic revision: r9 - 15 Oct 2010, UnknownUser
 

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