New Developments in Artificial Intelligence and the Semantic Web

1.4Q/A2.3.9.1 Influence modelEach Prolog program can be thought as an activecontrol flow, which has inputs and outputs on severallevels. In Figure 12 inputs (callers) are up andoutputs (callees) down. Pure logic, including temporaryeffects, is in the base line. A vertical distancefor each influence type can be defined as follows:Com-components are the most distant lines as wellas external actions that cannot be repeated. The mostdistant lines are main influences, compared withside effects that are intermediate data and not amongthe wanted results.callerFigure 10. User interface of JavaMaster.9 Prolog comprehensionVisual Prolog resembles Java in most informationneeds (Sections 3 and 5). It contains program flows,classes, objects and dependency models. Some essentialdifferences are non-determinism, strong recursivenature, declarative syntax, and flow analysis.Further, public attributes are not allowed and predicatesare forming much more compact units than inmethods of Java. Most of these differences makeunderstanding easier. From the programmers pointof-viewit would be best not to use facts, becausefacts can cause side effects, but it is not always possibleto avoid this.Understanding side effects is essential in Prolog(Walker et al 1997). In Figure 11 there are twocases, A and B, using predicates p, q and r. Predicatep causes a side effect note(X) to case A but notto B. It has direct influence on predicate q but not onr. Still, if r is called after q then B is dependent ofnote indirectly.Summary: The side effects can be detected completelyby symbolic analysis because the phenomenin Figure 11 is a control flow... p(X) | q(Y) | r(X,Y)assert(note(X))note(X),s(X)s(X)A: Side effects B: No side effectsFigure 11. Prolog’s side effect model.Startcallee• • •Figure 12. Prolog’s influence model.TargetThis model can be useful in planning refactoring forVip classes.9.2 Visual Prolog applicationIn order to understand a complete Vip applicationwe can use the following main approaches (the relatedfigure in parenthesis):• Static: How has it been written? (F. 11)• Dynamic: How does it behave? (F. 12)• Symbolic: What are the explanations for candidatesbetween starts and targets referring to ourfocus? (F. 10)The symbolic approach is the most general one. Itis pragmatic by nature. It could give us useful snapshotsfrom the user’s approach combining the dimensionsof Figure 3!10 ConclusionsA seamless architecture for a symbolic programcomprehension methodology has been described inthis paper. Using Visual Prolog proved to be a rightchoice. When one of the most characteristic featuresof traditional languages is that they are leading intomore and more specific applications, Visual Prologhas, as shown in this paper in Sections 2..9, becauseof its declarative notation, another rather valuablefeature; it is leading into wider, more abstract thinking,thus creating more general approaches andtheories related to the software science.New Developments in Artificial Intelligence and the Semantic WebProceedings of the 12th Finnish Artificial Intelligence Conference STeP 2006 140