The MIDAS System

The MIDAS System consists of two major parts:

• The command language  which enables the user to run programs and to communicate with the image displays  and the interactive graphic devices . The image display can be a peripheral device of your mainframe (e.g. DeAnza, Ramtek, ...) or a window on the screen of your workstation. The graphic device may be a graphics terminal connected to your main computer (HP, Tektronix compatible, ...) or again a window if you work on a workstation;
• The program interface, i.e. a set of subroutines/functions described in this document, which is used by the application programs to interface to terminals, to Bulk Data Frames (images), to tables, to obtain information from the image display and graphics device as well as the command language.

The reader should distinguish between the MIDAS system  described above and the MIDAS environment  which is the programming ``environment'' in which application programs are written and which uses the interfaces described here.

MIDAS knows three basic abstract data structures:

• Keywords , are variables which can be used to pass information from one MIDAS program to the next or to store intermediate results;
• Descriptors , are variables which describe the structure of the tables and images. They can also store any other auxiliary information connected to the data like histograms, RA and DEC values etc.;
• Data Values .

Combining descriptors and data yield the composite data structures:

• Bulk Data Frames   (usually called images), which are a set of data of physical significance. The set can have a certain dimensionality (in MIDAS up to three). The data can be stored in a wide range of formats on disk e.g. bytes, integers and reals. The default file extension of this data structure is .bdf;
• Tables , are structures for handling heterogeneous data sets which can be arranged in rows and columns. The default file extension is .tbl;
• Fit files , which contain the instructions for a fit process to be performed on a data structure. The default file extension is .fit.

These higher level structures can be organized and manipulated in a global manner by using catalogues containing four lists of data structures.

• Image Catalogues ;
• Table Catalogues ;
• Fit file Catalogues ;
• ASCII file Catalogues .

In order to access data structures or to pass or retrieve information from the user the MIDAS Environment provides the ST and TB, for Fortran,   and the SC and TC interfaces for C programs  . The following data structures can be accessed using the ST and TB (SC and TC) interfaces:

• Keywords;
• Descriptors;
• Bulk Data Frames;
• Catalogues;
• Tables.

In addition, the interfaces take care of the communication between MIDAS and the application program .

A general description of these interfaces is given in Chapter and . Appendix and provide the detailed interface descriptions.

Since the 94MAY release of Midas there is also a set of graphics interfaces, the PT (for Fortran) and PC (for C) interfaces included in the Midas environment.

A general description of these interfaces is given in Chapter , and Appendix provides the detailed interface descriptions.

Communication interfaces which support a client/server scenario have been added with the 94NOV release. These XC interfaces are only implemented for C and only for Unix (no plans to port them to Fortran and/or VMS).
Please, note, that this is a very first version of the XC interfaces. Therefore, we reserve the right to modify the XC interfaces in the future!

A general description of these interfaces is given in Chapter and Appendix provides the detailed interface descriptions.

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