AspectOriented Action Semantics Descriptions

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Aspect-Oriented Action Semantics Descriptions

• Luis Menezes
• University of Pernambuco
• (lcsm_at_dsc.upe.br)

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Agenda

• Action Semantics
• Aspect-oriented Programming
• Aspect-oriented Action Semantics
• Conclusions

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Action Semantics

• Formalism to describe programming languages
• Action Notation
• concepts of programming languages
• Based on English terms (intuitive)
• Hides the modeled concepts complexity

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Action Semantics

• Examples of actions
• give 1
• then
• give product(2,the given integer)
• bind x to 10
• hence
• give sum(1,the integer bound to x)
• allocate a cell
• then
• store 10 in the given cell

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Action Semantics Descriptions

• Originally AS descriptions are formed by
• Abstract Syntax
• Semantic Functions
• Semantic Entities
• This organization separates the description of
  each PL concept in these modules.

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Modular Extensions

• Proposed to increase the modularity of AS
  descriptions
• Object Oriented AS, Component AS, Modular AS
• Descriptions formed by a set of language elements
• Each element has syntax and semantics.
• Facilitates the identification where the PL
  elements are defined.

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Syntax-less Concepts

• Action Semantics descriptions translates
  syntactical elements into action notation.
• Some programming language concepts are not
  represented by textual code in programs.
• For example
• The code
• f(1 x) / y
• can be used by lazy or eager programming language
  
• Action Semantics Descriptions can not isolate
  their descriptions in separated modules
• The semantics is described inside other features
  semantics

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Example

• Expressions language
• component Constant is Exp where
• syntax nnumber
• semantics give n
• component Sum is Exp where
• syntax aExpression bExpression
• semantics
• (evaluate a and then evaluate b)
• then
• give sum of them

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Example

• Lazy Expressions Language
• component LazyConstant is Exp where
• syntax number
• semantics give abstraction of give n
• component LazySum is Exp where
• syntax aExpression bExpression
• semantics
• give abstraction of (
• (evaluate a and then evaluate b)
• then
• (enact the given abstraction 1 and
  then enact the given abstraction 2)
• then
• give sum of them
• )

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Traditional object-oriented system developing has
a similar problem.
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Crosscutting Concern

• Crosscutting concern is a system feature that
  affects other concerns
• They can not be implemented in a separated module
• Difficult to insert/remove in complex systems

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Crosscutting Concern

• Example Remote Databases
• void transfer(Account src, Account dest, int
  amount)
• if (!src.avaliable(amount))
• throw new TransferError()
• src.whitdraw(amount)
• dest.deposit(amount)

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Crosscutting Concern

• Example Remote Databases
• void transfer(Account src, Account dest, int
  amount)
• try
• DataBase d connect()
• d.openTransaction()
• if (!src.avaliable(amount))
• throw new TransferError()
• d.rpc(whitdraw,src,amount)
• d.rpc(deposit,dest,amount)
• d.closeTransaction()
• catch (CommunicationError e)
• d.undo()
• throw new TransferError()

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Aspect-oriented Programming

• Methodology designed to modularize the definition
  of crosscutting concerns
• Aspects
• Identify points in the system code
• Specify how these points are affected by the
  crosscutting concern implementation
• Weaving Operation
• Perform the modifications described by aspects

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Weaving Operation
void transfer(Account src, Account dest, int
amount) if (!src.avaliable(amount))
throw new TransferError()
src.whitdraw(amount) dest.deposit(amount)

aspect RemoteDataBase ..
Weaving
void transfer(Account src, Account dest, int
amount) try DataBase d
connect() d.openTransaction()
if (!src.avaliable(amount)) throw
new TransferError() d.rpc(whitdraw,src,
amount) d.rpc(deposit,dest,amount)
d.closeTransaction() catch
(CommunicationError e) d.undo()
throw new TransferError()
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Aspect-oriented Action SemanticsDescriptions

• Motivation
• Use aspects to improve the modularity of action
  semantics descriptions
• Operators designed to support aspect-oriented
  concepts in action semantics

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Advices

• Specifies a modification in the specification
• An advice can
• Modify the whole component semantics
• change semantics from x to y
• Rewrite a subterm inside the component semantics
• rewrite t1 to t2

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Advices
aspect A change semantics x to
complete and then x
component Constant is Exp where syntax
nnumber semantics give n
Weaving
component Constant is Exp where syntax
nnumber semantics
complete and then give n
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Pointcuts

• Constrains the advices
• Examples of pointcuts
• The advice acts in specific components
• inside c do a
• The advice needs a runtime condition to be
  enabled.
• a when c

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Advices
component Constant is Exp where syntax
nnumber semantics give n component
Identifier is Exp where syntax
iIdentifier semantic give the integer
bound to i
aspect A inside Identifier change
semantics x to complete and then
x
Weaving
component Constant is Exp where syntax
nnumber semantics give n component
Identifier is Exp where syntax
iIdentifier semantic
complete then give the
integer bound to i
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Example 1Lazy Evaluation Aspect

• compoent Constant is Exp where
• syntax number
• semantics give closure abstraction of
  give n
• component Sum is Exp where
• syntax aExpression bExpression
• semantics
• give closure abstraction of (
• (evaluate a and then evaluate b)
• then
• (enact the given abstraction 1 and
  then
• enact the given abstraction 2)
• then
• give sum of them
• )

Advice 1 Expressions gives functions instead
values
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Example 1Lazy Evaluation Aspect

• compoent Constant is Exp where
• syntax number
• semantics give closure abstraction of
  give n
• component Sum is Exp where
• syntax aExpression bExpression
• semantics
• give closure abstraction of (
• (evaluate a and then evaluate b)
• then
• (enact the given abstraction 1 and
  then
• enact the given abstraction 2)
• then
• give sum of them
• )

Advice 1 Inside Exp do change semantics
from x to give closure abstraction of
x
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Example 1Lazy Evaluation Aspect

• compoent Constant is Exp where
• syntax number
• semantics give closure abstraction of
  give n
• component Sum is Exp where
• syntax aExpression bExpression
• semantics
• give closure abstraction of (
• (evaluate a and then evaluate b)
• then
• (enact the given abstraction 1 and
  then
• enact the given abstraction 2)
• then
• give sum of them
• )

Advice 2 Evaluate the abstraction before to
execute data operations
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Example 1Lazy Evaluation Aspect

• compoent Constant is Exp where
• syntax number
• semantics give closure abstraction of
  give n
• component Sum is Exp where
• syntax aExpression bExpression
• semantics
• give closure abstraction of (
• (evaluate a and then evaluate b)
• then
• (enact the given abstraction 1 and
  then
• enact the given abstraction 2)
• then
• give sum of them
• )

Advice 2 inside Exp do rewrite give op(a)
to evaluateLazyData in a
then give op(them)
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Example 1Lazy Evaluation Aspect

• compoent Constant is Exp where
• syntax number
• semantics give n
• component Sum is Exp where
• syntax aExpression bExpression
• semantics
• (evaluate a and then evaluate b)
• then
• give sum of them

• aspect LazyEvaluation
• Inside Exp do
• change semantics from x to
• give closure abstraction of x
• inside Exp do
• rewrite give op(a) to
• evaluateLazyData in a
• then
• give op(them)

weaving
Lazy Expressions Language
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Example 2Static x Dynamic Binding

• Static Bindings
• component SB_FDecl is Decl where
• syntax iId () cCom
• semantics
• bind i to closure abstraction of
• semantics of c
• component SB_FCall is Com where
• syntax i Id ()
• semantics
• enact the abstraction bound to i

• Dynamic Bindings
• component DB_FDecl is Decl where
• syntax iId () cCom
• semantics
• bind i to abstraction of
• semantics of c
• component DB_FCall is Com where
• syntax i Id ()
• semantics
• enact closure the abstraction bound to i

aspect DynBind rewrite enact
x to enact closure x
aspect StaBind rewrite abstraction
of x to closure abstraction of x
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Example 2Static x Dynamic Binding
component FDecl is Decl where syntax iId
() cCom semantics bind i
to abstraction of semantics of
c component FCall is Com where syntax i
Id () semantics enact the
abstraction bound to i
aspect StaBind rewrite abstraction
of x to closure abstraction of x
aspect DynBind rewrite enact
x to enact closure x
weaving
weaving
Language with Static Bindings
Language with Dynamic Bindings
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Conclusions

• Aspects are useful to describe some programming
  language concepts improve the modularity describe
  
• Component libraries become more generic
• Future research in this topic includes
• Implementation of tools
• Define new aspect operators and applications to
  programming language research
• Design an aspect-oriented library of PL concepts

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Aspect-Oriented Action Semantics Descriptions

• Luis Menezes
• University of Pernambuco
• (lcsm_at_dsc.upe.br)