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This is a brief description of the Haskell implementation of Web Service
Algebra (Institut für Informatik, Universität Augsburg)

(c) December 2007 by Peter Höfner & Florian Lautenbacher

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0. Prerequisites
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The Package requires a Haskell implementation; please see 
http://www.haskell.org for download and installation guides.

We will assume that users of our implementation have at least 
a superficial knowledge of Haskell.



1. Package Structure
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The basic module is  WebService.hs . It is a proper Haskell 
module that needs to be imported into the definitions of 
particular feature algebras. Samples of usage are provided by
the file
    BusinessTrip.hs
This provides a implementation of a business trip example
discussed in the accompanying report "Algebraic Structure of Web Services" available from
http://www.informatik.uni-augsburg.de/lehrstuehle/dbis/pr/wsalgebra.html

To use the example, simply load the BusinessTrip.hs file
into your Haskell interpreter or compiler, i.e., 

    :l BusinessTrip.hs



2. Main Types and Functions
---------------------------

Each simple Web Service is typed as Rel [String] therefore the simple Web Service
can be set as a set [(set [data],set [data])], 

To reach an (extended) Web Service one needs to blow this simple Web Service up.

blow ws creates an extended Web Service and blows it up with additional information
blow t  blows up a test and extends it with additional data

buildplan creates a plan for a Web Service

Concatenation of Tests or Web Services can be achieved by using ##.
The negation of a test can be reached using neg.

The choice of Web Services is done using WS \/ WS

The (forward) diamond (|x>p) is modelled as fd (x) p, the (forward) box as fb (x) p.

The Kleene star (*) is described simply as star.



Hence, a query like not(etix+etix2); |flight*> |flight*] (etix;etix2)  could be modelled as

buildplan ((neg (t1\/t2))##(fd (star flight) (fb (star flight) (t1##t2))))



3. Further Usage
----------------

For outputting the result of a normalisation into a file and the like
the standard Haskell operations of result type IO() may be used; 
currently we do not provide special operations for this.


4. Feedback
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We are very interested in hearing from users. Please send your comments to

    hoefner@informatik.uni-augsburg.de or
    lautenbacher@informatik.uni-augsburg.de.