The SDSS Query Tool (sdssQT) is a Graphical User Interface (GUI) that provides the functionality necessary for SDSS users to prepare and submit queries to the Science Archive. It is written in Tcl/Tk version 8, which is a scripting language available on most computing platforms. It provides you with an interactive windowing environment where you can enter your queries. It does not include any visualization or graphical query preparation tools. The current version of the sdssQT is v2.3.1 (the current version always appears on the sdssQT's main window title bar).
An SDSS query must be formulated in a language we call SXQL (SDSS Extended Query Language). SXQL is a subset of SQL, the 'Structured Query Language' defined originally for relational databases. We chose to conform as closely to SQL as possible since it is a well-defined, powerful query language that has been in use for a long time. However, since the Science Archive is not a relational database but an object-oriented database, we can have only a subset of SQL with some object-oriented extensions and additional language macros which are very specific to astronomical data. There is a query language for object-oriented databases called OQL (Object Query Language), but none of the currently available commercial databases have an implementation of it yet. The SXQL is not OQL, but many features originate from the OQL specification document. It is a first step toward OQL in many respects.
The contents of this document are as follows:
Section 2 describes the usage of the SDSS Query Tool
Section 3 describes the SDSS Extended Query Language (SXQL) in detail.
Section 4 containts tips and example queries with explanations.
