UNDERSTANDING THE SYSTEM AND ITS PHILOSPHY

Before contributing to the system it is important that you are familiar with the system as a user, and get the `feel' of it. This is best done by reading the User Guide (USER_001), performing some analysis, and studying the two major programmer documents: PROG_002, which describes the standard datasets and conventions on which the system is based, and PROG_001, which specifies the rules for ASTERIX programming. You will also find the yellow ADAM user guide, SG4, useful if you are unfamiliar with ADAM/ICL.

The basic shape of the system is a set of instrument interfaces, and a body of instrument-independent software, here we concentrate on the latter. A guide to writing an instrument interface will be provided later as a separate document. An ASTERIX application should be:

• robust - it should make the minumum of assumptions about the nature and size of the input data. It should work whenever it is given enough information to proceed sensibly, making defaults as necessary, and warning the user wherever this seems appropriate.

• easy-to-use - it should provide a modest number of informative prompts (additional parameters may be invisibly defaulted in the interface file, and hence available to the expert user), with on-line help, and a detailed description of method and usage in the ASTHELP system.

• atomic - each application should perform one or a small number of jobs thoroughly, on a wide variety of different inputs. Separate functions should be implemented in separate programs, unless there is some very good reason to the contrary. This makes the system more flexible and comprehensible.