discussion with gregor kiczales at ubc

AO Mechanisms in Demeter 1

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.


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


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 JPMstatic JPM


range of AOP languages

means of … join points

JPM join points identifying specifying semantics at

AspectJ dynamic JPM

points in execution call, get, set…

signaturesw/ 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 signatures add, compose (and remove) members

Demeter traversals when traversal reaches object or edge

class & edge names

define visit method




add, compose (and remove) members

signaturesmembersHyper/J

add memberssignaturesclass members static JPM

Demeter traversals

Composition Filters

AspectJ dynamic JPM

JPM

types

message sends & receptions


join points

succinct traversal specs

signature & property based object queries


identifying

generate traversals

wrappers declarative (filters) imperative (advice)

advice

specifying semantics at

See next slide for changes to Demeter




JPM join points identifying specifying semantics at

AspectJ dynamic JPM



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

class members

class membersclass members

visitor method signatures

traversal spec. sclass graph g

class namesclass graph

visitor method bodies

s + g (result = traversal implementation)

add membersclass graph with tokens=grammar (result = parsing and printing implementation)




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


join points

visitor method signatures

source and targets of traversal

trav. spec. sclass graph gobject graph o


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


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.


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.


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


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.


• 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]


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


Masuhara/Kiczales Modeling Framework for AO Mechanisms

• X• X[JP]• A• A[ID]• A[Eff]• B• B[ID]• B[Eff]• META


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


Demeter static JPM 2: Open Classes

See paper.


Demeter static JPM 3: special case of Open Classes

• X– Combined program

• X[JP]– c declarations

• A– c declarations including the class graph


• 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


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[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


Demeter dynamic JPM 2: special case of TRAV

For methods fetch, gather and asList: special advice


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.

• 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[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

Demeter dynamic JPM 4: DJ with Functional Visitor

Taken apart


Conclusions

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

discussion with gregor kiczales at ubc

Documents

join pointsin aspectjpoints

dynamicvisitor jpm

point model jpm

result of traversal

membersclass graph

demeterao mechanisms

traversal implementation

point modelstraversal