For an information source, there are four layers of a description:
1. What queries it can answer. For a database, this would usually be determined by the database query language (SQL or others). However, the queries that can be answered by a particular website are usually very limited. The XIB needs to provide a grammatical nontation for specifying the set of queries that can be submitted.
2. What information it can provide. This is the output data we expect from the information source, specified in a XML DTD.
3. Where is the information source. For our purposes, this may be the URL of a cgi script for a website, or the URL address of a database server.
4. Where is the data exactly located.
For a database, this is specified in the database schema. For a website, on
the other hand, pertinent data is usually hidden inside an HTML document, so we need to
specify the exact location of those data.
We shall call these four components of information source description INPUT, OUTPUT, INPUT BINDING and OUTPUT BINDING, respectively. There is also an additional element called DESCRIPTION that is simply a description of the information source. To illustrate the construction of XIB Descriptions, we have two examples:
| AmazonSearch (Web Based Information Source) |
ConverterDBService (Database Information Source) |
| INPUT | INPUT |
| OUTPUT | OUTPUT |
| INPUT BINDING | INPUT BINDING |
| OUTPUT BINDING | OUTPUT BINDING |
| Complete Description | Complete Description |