XML encoding of tabular information

6 Copyright © 2010 Open Geospatial Consortium

6.2 XML encoding of tabular information

The data access operations b,c,d, and e above return selected parts or all of an XML encoded data file, in a format known as Geographic Data Attribute Set GDAS. The GetData operation returns an entire GDAS file including attribute data and its associated metadata, while DescribeFrameworks, DescribeDatasets, and DescribeData each return selectively larger portions of the metadata for the geographic attributes that can be obtained from the TJS server. At the other end of the data exchange process, the JoinData operation accepts attribute data in GDAS format. The purpose of the Geographic Data Attribute Set GDAS encoding format is to package attribute information and its associated metadata so that it can be transmitted across a network. The GDAS format offers the following benefits: · It is simple to understand and implement. The core of the encoding has a similar structure to the encoding for an HTML Table. This makes the file easy to generate from corporate database technology, and easy to manipulate into other encodings such as HTML using XSLT. It also facilitates debugging. · It is lightweight. The encoding was designed to be as light-weight as possible, in order to minimize network transmission times for large datasets without introducing the overhead of data compression. · It is highly scaleable. The encoding can carry multiple attributes simultaneously, with minimal additional overhead. · It is multi-purpose. The encoding can represent all types of attribute data, allowing a generic interface to handle all types of attribute data. · It is unambiguous. The encoding uniquely references the framework dataset to which the attributes apply. · It contains substantial metadata, which makes it possible to automatically generate tables, charts, documentation, maps, and legends from the same data stream. · It supports the identification of null values in the dataset to facilitate their exclusion from calculations and legends · It includes attributes to support the joining of tabular data to geometry in an N:1 or N:N fashion. · It specifies an attribute typology that facilitates the automated determination of appropriate forms of mapping and charting. The GDAS format is designed to support simple as well as rich and complicated attribute databases that may not always be easy to interpret. The metadata included in the encoding is designed to ensure that the user knows exactly what the content of the dataset is as well as which spatial framework it references, and has easy access to any associated documentation. GDAS is only ever produced in its entirety as the response to a TJS GetData request, but portions of GDAS underlie all TJS operation requests and responses. Copyright © 2010 Open Geospatial Consortium 7

6.3 Uses of GDAS and TJS