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AUML*Notation

To support the modeling phase, the developed framework includes a graphic notation, called AUML+, supported by a visual modeling tool. The proposed notation is an extension of the notation used in the AUML initiative Protocol Diagrams, which has also been furnished with formal semantics. The Protocol Diagrams proposed by the AUML initiative are extremely helpful for designing IPs. This notation can express:

  • The agents and/or roles that participate in the interaction.
  • All the exchange sequences in which an agent can participate throughoutthe interaction, possibly simultaneously.
  • The connections between these exchange sequences: alternatives, options, iterations and simultaneity.
  • The message exchanges that occur in each sequence.
  • The conditions under which these exchanges occur.
  • The characterization of the exchanges: multiplicity(unicast, multicast, broadcast), message sending type (delayed, multicast, broadcast) and concurrency type.
  • Definition of synchronization points.
  • Protocol composition from other protocols by interlinking or embedding to promote modularity.
  • Parameterization of protocols to promote reuse.

Nevertheless, while AUML notation is fine for providing a simple representation of the designers view of an IP, it is a basic and semiformal notation (just consider the widespread use of informal annotations). It is, therefore, inadequate as a starting point for automatically outputting the syntactic expression of the IP in a formal specification language as developed in the proposed framework.

First, we had to extend AUML notation to include other important aspects that need to be taken in account in complex interactions:

  • Correlation and causality Generally, agents participate in more than one dialogue at the same time. Therefore, relationships of correlation and causality between messages need to be speci¯ed so that each message can be associated with the specific IP instance to which it belongs, and messages from different IPs involved in the interaction can be related.
  • The time factor The time factor needs to be considered in IP design. It should be possible to specify a pause between exchanges for a finite time and establish deadlines for both an exchange sequence and for the global interaction.
  • Protocol exceptions Apart from describing the basic message exchange pattern, a protocol diagram should also consider the interaction flow triggered by the occurrence of a protocol exception as a result of out-of-sequence message reception, message loss, time-outs, etc.
  • Event management An IP should consider the occurrence of given events as triggers of a given exchange pattern.
  • Compensation protocols It should also be possible to express transactional contexts within the main exchange pattern and associate compensation protocols (cancellations, renegotiations, etc.) with such contexts.

Figure 1 shows a screenshot of the AUML*2ACSL tool which has been developed as part of the proposed framework. It illustrates the Iterated Contract Net protocol design, proposed by FIPA [17], in AUML* notation. The symbol palette shows the new constructs.

 

auml2acsl Iterated Contract Net Contract Net Protocol
Figure 1: AUML*2ACSL tool screenshot for Iterated Contract Net protocol
(Download Visio AUML*2ACSL file click)

auml2acsl Iterated Contract Net Sian Protocol
Figure 2: AUML*2ACSL tool screenshot for Sian protocol
(Download Visio AUML*2ACSL file click)

Apart from the AUML extension, this notation had to be formalized semantically as a provision for formalizing the other views of the proposed framework, principally the specification view. To be able to output an ACSL specification, we needed a lot of information not covered in the notation proposed by AUML or, alternatively, expressed informally by annotations, apart from additional constructs not included in AUML notation. Figure 2 also shows a dialogue including some semantic elements associated with an ACL counterPropose exchange.

 
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