Polyglot: multiple interpreters for BeepBeep 3

This package contains a front-end to the BeepBeep 3 event stream query engine. This front-end provides multiple interpreters reading expressions in various specification languages, and converting them into the equivalent chain of BeepBeep processors.

It currently provides interpreters for the following notations:

• Linear Temporal Logic (LTL)
• LOLA
• Quantified Event Automata (QEA)

In all cases, the interpreter extends the capabilities of the original languages by adding other features supported by the BeepBeep event stream engine, thereby generalizing each specification language.

Table of Contents {#toc}

• The LOLA interpreter
• About the author

The LOLA interpreter {#lola}

Suppose that exp is a string variable containing the following LOLA specification:

s1 = true
s2 = t3
s3 = t1 | ((t3) < (1))
s4 = ((t3)^(2) + (7)) mod 15
s5 = ite(s3; s4; (s4) + (1))
s6 = ite(t1; (t3) < (s4); !(s3))
s7 = t1[+1; false]
s8 = t1[−1; true]
s9 = s9[−1;0] + t3
s10 = t2 | (t1 & s10[1; true])

Consider the following piece of code:

LolaInterpreter lol_int = new LolaInterpreter();
NamedGroupProcessor ngp = (NamedGroupProcessor) lol_int.parse(exp);
Processor t1, t2, t3; // Define these processors ...
Connector.connect(t1, 0, ngp, ngp.getInputIndex("t1"));
Connector.connect(t2, 0, ngp, ngp.getInputIndex("t2"));
Connector.connect(t3, 0, ngp, ngp.getInputIndex("t3"));
Pullable p = ngp.getPullableOputput("s10");
while (p.hasNext()) {
  ...
}

This code does the following:

1. Create a new LOLA interpreter
2. Parse the LOLA specification from a string
3. Since the streams t1, t2 and t3 are considered as input streams in the specification, associate them to actual sources of events
4. Get a hold of the Pullable object corresponding to the output of s10
5. Iterate over events output by s10

That's it! As one can see, this interpreter is just an alternate way of instantiating and piping BeepBeep processors, using the syntax of the LOLA language.

Features {#features}

Since the interpreter is simply a front-end to BeepBeep, many constructs not present in the original LOLA have been added to the language. We list a few of them here.

Window functions

The construct win(fname, streamname, w) can be used to denote the application of function fname on a sliding window of width w from the events of streamname. For example, the cumulative sum is computed by replacing fname by sum. Virtually any function can go in place of fname.

Mutator

One can turn an arbitrary stream s into a stream of the same constant k by writing convert s into k. This corresponds to the Mutator processor in BeepBeep.

About the author {#about}

The BeepBeep interpreters were written by Sylvain Hallé with contributions from Raphaël Khoury, both professors at Université du Québec à Chicoutimi, Canada.