AO Mechanisms in Demeter1 Discussion with Gregor Kiczales at UBC Ontology of AOP Ontology is the study of what there is, an inventory of what exists. An ontological commitment is a commitment to an existence claim for certain entities. Slides and the last one are Gregor’s An ontology is, in simple terms, a collection of concepts with relations among them plus constraints on the relations.

AO Mechanisms in Demeter2 basis of crosscutting a join point model (JPM) has 3 critical elements –what are the join points in AspectJ –points in runtime call graps members –means of identifying join points in AspectJ –signatures (plus …) –means of specifying semantics at join points in AspectJ –advice –define members

AO Mechanisms in Demeter3 basis of crosscutting a join point model (JPM) has 3 critical elements –what are the join points in AspectJ –points in runtime call graph –class members –means of identifying join points in AspectJ –pointcuts –member signatures (plus …) –means of specifying semantics at join points in AspectJ –advice –define members dynamic JPM static JPM

AO Mechanisms in Demeter4 range of AOP languages means of … join points JPMjoin pointsidentifyingspecifying semantics at AspectJ dynamic JPM points in execution call, get, set… signatures w/ wildcards & other properties of JPs advice static JPMclass memberssignaturesadd members Composition Filtersmessage sends & receptions signature & property based object queries wrappers declarative (filters) imperative (advice) Hyper/Jmemberssignaturesadd, compose (and remove) members Demeter traversalswhen traversal reaches object or edge class & edge names define visit method

AO Mechanisms in Demeter5 range of AOP languages means of … join points add, compose (and remove) members signaturesmembersHyper/J add memberssignaturesclass members static JPM Demeter traversals Composition Filters AspectJ dynamic JPM JPM types message sends & receptions points in execution call, get, set… join points succinct traversal specs signature & property based object queries signatures w/ wildcards & other properties of JPs identifying generate traversals wrappers declarative (filters) imperative (advice) advice specifying semantics at See next slide for changes to Demeter

AO Mechanisms in Demeter6 range of AOP languages means of … join points JPMjoin pointsidentifyingspecifying semantics at AspectJ dynamic JPM points in execution call, get, set… signatures w/ wildcards & other properties of JPs advice static JPMclass memberssignaturesadd members DemeterJ, Demeter/C++ dynamic JPM static JPM 1 static JPM 2 static JPM 3 when traversal reaches object or edge class members visitor method signatures traversal spec. s class graph g class names class graph visitor method bodies s + g (result = traversal implementation) add members class graph with tokens=grammar (result = parsing and printing implementation)

AO Mechanisms in Demeter7 range of AOP languages means of … join points add memberssignaturesclass members static JPM DJ dynamic JPM 1 dynamic JPM 2 dynamic JPM 3 AspectJ dynamic JPM JPM when traversal reaches object or edge (method traverse) when traversal reaches object (methods fetch, gather, asList) nodes in object graphs points in execution call, get, set… join points visitor method signatures source and targets of traversal trav. spec. s class graph g object graph o signatures w/ wildcards & other properties of JPs identifying visitor method bodies method name (fetch, gather, asList) s+g+o(result = traversal implementation = edges to traverse at nodes in object graph) advice specifying semantics at

AO Mechanisms in Demeter8 Composing join point models Traversal Spec JPM: In Demeter we use traversal specifications and the class graph to define a traversal implementation (either static or dynamic) Visitor JPM: The result of Traversal Spec. JPM is used to define a second JPM: –The traversal implementation defines nodes and edge visits. –Visitor signatures define the nodes and edges where additional advice is needed: they are the means of identifying join points. –The means of specifying semantics at join points are the visitor bodies.

AO Mechanisms in Demeter9 DJ: dynamic JPM 3 The join points are nodes in object graphs. They are not dynamic call graph join points nor class members! The means of identifying the join points for a given object graph o are a strategy s and the class graph g. o must conform to g. The means of specifying the semantics at the join points are again s and g. See paper with Mitch Wand for the formal details behind this JPM.

AO Mechanisms in Demeter10 DemeterJ: static JPM 1 The means of identifying the join points and of specifying the semantics at the join points are the same. The reason is that s+g both –select the classes that will get traversal semantics –determine the details of the traversal semantics

AO Mechanisms in Demeter11 DemeterJ: static JPM 3 The means of identifying the join points (class members) is done by the class graph. When we add tokens to the class graph we get a grammar that contains instructions for parsing and printing behavior. A grammar is an aspect (external representation aspect): the adhoc implementation cuts across all classes.

AO Mechanisms in Demeter12 foo –dynamic JPM (~ AspectJ) –what happens in pattern bar AO design in UML Composition Patterns –static JPM (~ Hyper/J) –binds pattern to base code UML class & interaction diagrams already crosscut –by-class vs. by-interaction organizations [Clarke, Walker]

AO Mechanisms in Demeter13 Masuhara/Kiczales Modeling Framework for AO Mechanisms A and B: languages X: result domain of weaving process X[JP]: join points in X A[ID], B[ID]: identify join points in X A[Eff], B[Eff]: effecting semantics at jps META: parameterize weaving process

AO Mechanisms in Demeter14 Masuhara/Kiczales Modeling Framework for AO Mechanisms X X[JP] A A[ID] A[Eff] B B[ID] B[Eff] META

AO Mechanisms in Demeter15 Demeter static JPM 1: special case of Open Classes X –Combined program X[JP] –c declarations A –c declarations including the class graph A[ID] –Method signatures A[Eff] B –Traversal specifications B[ID] –c names B[Eff] META –Traversal semantics: rules for translating traversal specifications to methods Adds traversal methods to a set of classes

AO Mechanisms in Demeter16 Demeter static JPM 2: Open Classes See paper.

AO Mechanisms in Demeter17 Demeter static JPM 3: special case of Open Classes X –Combined program X[JP] –c declarations A –c declarations including the class graph A[ID] –Method signatures A[Eff] B –Class dictionary (class graph enhanced with tokens defining the syntax addition) B[ID] –c names B[Eff] META –rules for translating class dictionary to parsing methods Adds parsing methods to a set of classes

AO Mechanisms in Demeter18 Demeter dynamic JPM 1: special case of Pointcuts and Advice X –Traversal execution X[JP] –Arrival at each object and has-a edge A –Traversal methods A[ID] –Method signatures A[Eff] –Execute traversal method body B –Visitor method declarations (serves as advice) B[ID] –Visitor method signatures (serves as pointcut) B[Eff] –Execute visitor method bodies META –none Adds advice to traversal methods

AO Mechanisms in Demeter19 Demeter dynamic JPM 2: special case of TRAV For methods fetch, gather and asList: special advice

AO Mechanisms in Demeter20 Demeter dynamic JPM 3 X –Object graphs X[JP] –Nodes in object graphs A –Class graph A[ID] –Class names A[Eff] B –Traversal specification B[ID] –Class names B[Eff] –Edges to traverse at node in object graph META –Rules for traversal order: depth-first, breadth-first, left-to-right, etc.

AO Mechanisms in Demeter21 Conclusions The Modelling Framework by Masuhara/Kiczales nicely captures the different AO mechanisms worked on by the Demeter team.