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 2 - 5 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 Demeter

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 signatures (plus …) means of specifying semantics at join points advice define members AO Mechanisms in Demeter

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 pointcuts member signatures (plus …) means of specifying semantics at join points advice define members dynamic JPM static JPM AO Mechanisms in Demeter

range of AOP languages means of … join points JPM join points identifying specifying semantics at AspectJ dynamic JPM points in execution call, get, set… signatures w/ wildcards & other properties of JPs advice static JPM class members signatures add members Composition Filters message sends & receptions signature & property based object queries wrappers declarative (filters) imperative (advice) Hyper/J members add, compose (and remove) members Demeter traversals when traversal reaches object or edge class & edge names define visit method AO Mechanisms in Demeter

See next slide for changes to Demeter range of AOP languages means of … join points add, compose (and remove) members signatures members Hyper/J add members class 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 Demeter

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

range of AOP languages means of … join points add members signatures class 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 Demeter

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 Demeter

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 Demeter

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 Demeter

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 Demeter

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

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 Demeter

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

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 Demeter

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

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 Demeter

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 Demeter

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

Demeter dynamic JPM 3 X X[JP] A A[ID] A[Eff] B B[ID] B[Eff] META Object graphs X[JP] Nodes in object graphs A Class graph A[ID] Class names A[Eff] B Traversal specification B[ID] 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 Demeter

Mixes two models together Demeter dynamic JPM 4: DJ with Functional Visitor X Traversal execution with runtime control (Subtraversal.apply(..)) X[JP] Arrival at each object (Functional Visitor only available to nodes) A Regular Java Program (class/fields declarations) A[ID] Class/fields signatures A[Eff] Provide reachability (my understanding is to construct object graph conforming to the class graph) B Traversal specification and visitor method declarations (including the default one: combine(..)) B[ID] Visitor method signatures (or the built-in semantics, for the combine(..)) B[Eff] Execute the visitor methods and compute and combine the values and provide the runtime control over the traversal(subset of the traversal graph computed from the traversal specification) META Mixes two models together

Demeter dynamic JPM 4: DJ with Functional Visitor X Traversal execution with runtime control (Subtraversal.apply(..)) X[JP] Arrival at each object (Functional Visitor only available to nodes) A Regular Java Program defining traversals (class/fields declarations) A[ID] Method signatures A[Eff] Execute traversal method body B Visitor method declarations (including the default method: combine(..)) B[ID] Visitor method signatures (or the built-in semantics, for the combine(..)) B[Eff] Execute the visitor methods and compute and combine the values and provide the runtime control over the traversal META Taken apart

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