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Paper: Querying Multiple Databases with StarView
Volume: 61, Astronomical Data Analysis Software and Systems III
Page: 96
Authors: Williams, J.
Abstract: StarView is the user interface to the Space Telescope Science Institute's Hubble Data Archive(HDA). It offers unique capabilities in exploring large scientific databases. These include creating custom queries without requiring the user to understand the structure of the database and the ability to work with multiple databases. These capabilities can be combined to allow for limited cross correlation between different databases in a single query. The goal of this presentation is to show what is required to make this happen. These unique abilities are grounded in the core design of StarView. First of all, StarView was designed to work with any relational database. Currently, StarView has been demonstrated with different Sybase databases that are accessed through the Space Telescope Database (STDB) interface. This flexibility is accomplished through the use of StarView's Data Definition Language (DDL). The DDL is used to describe each attribute in the database. The attribute description contains such information as data type, constraints and textual information. It may also specify associated attributes. The textual information additionally supports context sensitive help on the attributes. The ability to formulate custom queries is a fundamental part of StarView. The user can select the attributes he wishes to query on without needing to understand the structure and joins of the database tables. The custom query facility has its own DDL (known as Quick DDL) which describes relationships within a database. It can also describe relations between databases. This is how StarView supports a single query across multiple databases. As long as a relationship is defined in the DDL, a query can be generated. The user can create a custom query on the fly, or create a new form for querying using StarView's Form Definition Language (FDL). The changes needed to StarView to add a new database are relatively straight forward. To add a database, you must create new DDL for both StarView and the custom query facility. This is a simple process for single table databases. You do not have to make any changes to the user interface unless you want to create a new form. Once the DDL is added, the custom query facility can automatically be used to generate a query. If you do want a custom form, one can be created in FDL. That's all there is to it. An example of this is illustrated by adding a database of accepted ROSAT observations to StarView. Details of the DDL and query generation will be described. The results of a single query that operates simultaneously against the new database and DMF will be shown. Joining multiple databases is simple enough if you are doing an equijoin between databases. The problem is more complex when you want to perform a ``fuzzy join'' on position across databases. We will describe the work that is being done in StarView to address this issue.
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