DATA SELECTION REQUIREMENTS

This section describes how an analysis tool can select data and events 
from a stream of identically structured events.  We have the following 
requirements:

Scripting Language
--------------

1.  The analysis tool should include a full featured scripting language,
    as commonly understood, and as outlined below.

2.  The scripting language should have some understanding of events as objects, 
    as opposed to some simpler structure, such as arrays of numbers.  The 
    analysis tool's object model should be compatible with standard 
    object oriented programming languages, such as C++.  Note that PAW's 
    columnwise ntuple event model does not really meet this requirement.

3.  The scripting language should be able to extract data (as built-in data 
    types or subobjects) from events objects for histogramming, printing, 
    or other processing.

4.  The scripting language should be able to express complex mathematical
    expressions using event data.

5.  The scripting language should have debugging facilities.

6.  It should be possible to interface the scripting language to dynamically
    linked compiled high level languages, such C, C++, or Fortran.

Selection
---------

7.  It should be possible make decisions and to program selection criteria 
    based on event data using data extracted by any of the above methods, 
    so that only selected events are histogrammed, output, or subjected 
    to some kind of further processing.

8.  The analysis tool should be able to display selection criteria as
    text (on histograms or for printed output, etc.).

I/O
---

9.  The analysis tool should support its own object I/O format.

10.  The analysis tool should include libraries that allows its own format 
     object files to be read or written from compiled programs.

11.  The analysis tool should be able to read or write object files in 
     foreign formats using (user supplied) extrenal modules.

12.  The scripting language should be able to write selected event objects 
     to one or more output streams based on arbitrary selection criteria.

13.  The analysis tool should provide an object definition language
     and/or be able to define new object formats programmatically.

14.  From the previous criteria, it should be possible within the scripting
     language to read events in one format, convert and write them out
     in a different format.

15.  The analysis tool should support "virtual streaming," which means
     that it can tag a set of selected events, and read them back, without 
     physically writing them to a separate output stream.