# PERA: package for extended relation algebras

PERA is a set of files programmed in
Maple
allowing to use relation algebras extended with a neighborhood
structure.

It allows to describe relational algebras, use them (through
composition of inverse tests for instance) and manipulate them
(through product, weakening or interval composition).
## The relation algebra structure

PERA deals with (binary) relation algebras extended with a
neighborhood structure.

For a very simple presentation (in french) look at
[Euzenat 1998a]. For
more information, one can consult the Maple worksheet which contains
more references.
## What can be done

A good example of what can be done with PERA is provided in the
PERA worksheet.
For those non familiar with Maple, the PostScript version of the worksheet is
provided here.
To sum up, PERA allows to:

- Create an extended relation algebra;
- Use it through its operators (composition, inverse, neighborhood,
upward and downward granularity);
- Build a new extended relation algebra through product (soon), interval,
weakening and restriction;
- Rename the relations of an algebra;
- Compare algebras for equality or "containement";
- Various other tools (pointisable computation (buggy), etc.).

It does not implements constraint satisfaction algorithms for testing
satisfiability or finding the minimal labels.
It does not either consider the inference of granularity conversion
operators by any automatic mean (but maybe...).

## Maple specifics

This is not a package in the MAPLE sense.
## Where to download the package

Here
you an get the set of files for the current version (1.0) in compressed
format. It includes:

- pera.html
- This file
- pera
- the system
- a3xx
- Algebra of relations for point algebras (with branching past
and future);
- a13
- Algebras of relations for interval algebra (Allen);
- pera.ms
- A worksheet displaying the features of the package;
- pera.ps
- The PostScript output of the former (which displays a bug in pointisable).

http://exmo.inria.fr/software/pera/pera.html