Uses of GDAS and TJS

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6.3 Uses of GDAS and TJS

GDAS was designed to support the joining of tabular data to its spatial framework, for the purpose of populating OGC Web Map Service WMS or Web Feature Service WFS servers with additional attribute information. TJS can be configured to convert attribute and related information from GDAS format into the databases and configuration files required to support these other OGC services. GDAS can also be used as the response to a WMS GetFeatureInfo request. For example, once GDAS data has been sent and joined to a layer supporting a WMS server, this server can respond with a WMS GetFeatureInfo request with the requested subset of records in GDAS format. To accomplish this, GetFeatureInfo must specify “INFO_FORMAT=textxml; subtype=gdas1.0” as part of the WMS GetFeatureInfo request. The utility of TJS goes beyond the simple extraction and joining of database content, since data in GDAS format can be readily manipulated as part of a service chain. Services such as the OGC’s Web Processing Service WPS can be used to perform calculations, comparisons, or other analysis on attribute data in GDAS format before it is accessed by a JoinData operation. Since GDAS is quite a simple encoding, it can easily be used as an input or generated as an output from any spatial model. Furthermore, the incorporation of an XSL reference allows the same GDAS file to be used to generate web pages as well as to provide the input to models or automated mapping services. Although TJS was originally intended be configured with the tabular data housed on one server and the spatial framework data housed on another server, the Interoperability Experiment conducted by OGC in 2007 demonstrated that in some circumstances TJS is useful even when the attributes and spatial frameworks are housed on the same server. This is especially true for very large datasets, such as Census data, where user-triggered automated mapping can be deployed through the implementation of TJS. The data access operations are designed to support access to very large volumes of metadata without overloading the network connection. Note that while GDAS files can be served up dynamically via a TJS, for performance reasons it may be preferable to store the content of specific GetData responses and host them as static files. Deployment of such static GDAS files are also a valid way to provide canned or pre-processed data interpretations without the effort and expense of supporting a full-blown TJS implementation.

6.4 Relationship of TJS to other OGC standards