## 1. Introduction to Footprint Services

The Footprint Services for the Virtual Observatory consit of two main parts: a large, distributed database of spatial object spectra and a collection of tools for common spectrum processing.tasks. Unlike traditional programs, Spectrum Services are not to install on your own machine, but to access via the Internet. Spectrum Services provide a web interface that you can access with traditional web browsers and perform simple operations, like querying databases and displaying results. All scientific functions are available on the web interface, however to exploit the full potential of the services it is advised to use XML web services. XML web services are new platform independent technologies designed to access remote functions programatically. This technology is available for most of the programming languages but using modern languages, like Java or c# is suggested. You can read more about XML web services in Chapter 2.

Spectrum Services are using a data model designed according to a wide range of criteria. Spectra are stored in a high performance relational database server to allow very fast and sophisticad search. It is only required to be familiar with the underlying database schema if you want to write SQL queries for special purposes, all typical search operations are accessible using pre-built forms and web service functions. Database schema is described in Chapter 5.

Spectrum Services also define a data model for representation of spectra and spectral energy distributions (even time series). This data model is desingned by two points of view. One is to cover the needs of most kinds of astronomers from the supernova researchers to radio astronomers; the other is to give an easy-to-use and easy-to-understand object oriented interface for the programmers. The result of the endeavour is a proposal for an IVOA standard of astronomical spectral data representation which is fully implemented in the Spectrum Services. You can read more about the data model in Chapter 3.

Spectrum Services support retrieval of data in VOTable using the SSA interface, and FITS serialization is also planned. To learn more about SSA see Chapter 8.