LibBig

The library aims to offer an implementation of bigraphical reactive systems but also to provide some tools and the infrastructure for extending them or implement the brand new flavours of bigraphs in order to meet requirements of a wider spectrum of scenarios.

Part of this extensibility is achieved thanks to the attached properties which allows to dynamically extend the structure of bigraphs by attaching attributes or properties (thay may be mutable) to e.g. nodes. For instance, attached properties can be used to store concrete values such as ip addresses or user permissions without the need to encode all this information in the standard bigraphical language reducing the burden of the encoding and resulting in a streamlined model without loss of information thanks to this new layer of abstraction. Matchings and rewritings can be customised to take into account also attached properties and hence, the need to re-implement the whole bigraph framework to meet particular use cases is drastically reduced.

The library provides a default implementation of bigraphs. The classes Bigraph and BigraphBuilder provides methods for assembling bigraphs programmatically but importers from some textual representations are offered. Milner’s algebra is supported in the form of methods exposed by Bigraph and BigraphBuilder implementing operations (such as composition, juxtaposition, or nesting) and elementary bigraphs (such as identities or ions). However, BigraphBuilder can be used to modify bigraphs more freely by not necessarily constructive operations.

For instance, the following code snippet yields an object describing the bigraph pictured below:

	BigraphBuilder builder = new BigraphBuilder(signature);
OuterName spooler = builder.addOuterName("Spooler");
OuterName network = builder.addOuterName("Network");
Root root = builder.addRoot();
Node printer = builder.addNode("Printer",root,spooler,network);
builder.addSite(root);
builder.addSite(printer);
builder.addInnerName("Network",network);
Bigraph bigraph = builder.makeBigraph();
							

Attached properties can be used to dynamically attach additional information. For instance, the printer node can be decorated with the default paper format or its network alias:

	printer.attachProperty(new ProtectedProperty<String> ("NETWORK_ALIAS","Lab printer"));
							

Properties can be easily read:

	Paper format = printer.<Paper>getProperty("DEFAULT_FORMAT").get();
							

or written:

	printer.<Paper>getProperty("DEFAULT_FORMAT").set(Paper.A4);
							

Much of the information expressible by attached properties can be easily encoded in the bigraphical language, but there are cases requiring to extend (and hence re-implement) the bigraphical machinery. For instance, spatial information can be represented bigraphically, but in a rather abstract way. What if we are interested in the nearest printer or in the access point with the strongest signal? The following concise example illustrates how the matcher can be instructed to consider access points (nodes decorated with the “AP_C” control) within the range.

	Matcher matcher = new Matcher(){
	  protected boolean areMatchable(Bigraph agent, Node nodeAgent, Bigraph redex, Node nodeRedex) {
	      if(super.areMatchable(agent,nodeAgent,redex,nodeRedex)){
	          if(nodeAgent.getControl.equals(AP_C))
	              return checkDistance(nodeAgent);
	          else
	              return true;
	      }
	      ;return false;
	  }
	};
	for(Match m : matcher.match(bigraph,redex)){
	    doSomethingWithThisMatch(m);
	};
							

However optimal solutions are supported too:

	Matcher matcher = new WeightedMatcher(){
	    protected int matchingWeight(Bigraph agent, Node nodeAgent, Bigraph redex, Node nodeRedex) {
	        if(nodeAgent.getControl.equals(AP_C) && nodeRedex.getControl.equals(AP_C))
	            return getDistance(nodeAgent);
	        else
	            return super.matchingWeight(agent,nodeAgent,redex,nodeRedex);
	    }
	};