ArchJava

Connecting Software Architecture to Implementation

13/03/2012

University of St Andrews

Software Architecture (recap)

• Software architecture

describes the structure of a system

Enabling more effective design, program understanding, and formal analysis

Existing approaches decouple implementation code from architecture

Leads to inconsistencies, confusion, violation of architectural properties

Inhibits software evolution

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Software Architecture Recap(cont’d)

• Software system collection of

components,

their connections

• Showing constraints on component interaction

• Describing architecture in formal ADL’s

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ADL’s (briefly)

• ADL’s aid in specification and analysis of high level designs

• Existing ADL’s loosely coupled to implementation languages causing problems in analysis, implementation, understanding and evolution

• No guarantee that implementation code obeys architectural constraints

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Module Interconnection Languages(MIL)

Support system decomposition from separate modules

ADL’s make connectors explicit to describe data and control flow between components

MIL’s describe the uses relationship between modules

But MIL’s provide encapsulation by hiding names

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ArchJava

• ArchJava is an extension to Java that

• seamlessly unifies software architecture with implementation,

• ensuring that the implementation conforms to architectural constraints.

• Guarantees communication integrity between an architecture and its implementation

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ArchJava seamlessly unifies architectural structure and implementation in one language

allowing flexible implementation techniques

ensuring traceability between architecture and code, and

supporting the co-evolution of

architecture and implementation.

ArchJava

University of St Andrews

ArchJava

Guarantees communication integrity even in presence of advanced architectural features like run time component creation and connection

Similar to Darwin which supports dynamic changes in distributed architectures

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ArchJava Cont’d

• Key benefits

include better program understanding,

reliable architectural reasoning about code

keeping architecture and code consistent as they evolve,

encouraging more developers to take advantage of software architecture.

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• Introduces new language constructs

components

connections

ports

• These constructs work together to express software architecture

ArchJava

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• Language constructs

A component is a special object that communicates with other components in a structured way. Is an instance of the component class

Components communicate at same level through explicitly declared ports

Regular method calls not allowed

ArchJava

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• Language constructs

A port represents a logical communication channel between a component and one or more components its connected to

Ports declare 3 methods specified using requires, provides, and broadcasts keywords

ArchJava

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• Provided method implemented by component and available to other components connected to the port

• Required method provided by other components to this port

• Broadcast methods similar to required methods but can be connected to any number of implementations

ArchJava Language constructs

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This port design specifies services implemented by a component and services required by a component to do it job

Required interfaces make dependencies explicit

Ports also make it easier to reason about components communication patterns

Abstract design allows specification and type checking before implementation starts

ArchJava Language constructs

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• Connections

Connection consistency checks ensure that each required method is bound to a unique provided method

Alternative connection semantics implemented by writing ‘smart connector’ components

ArchJava Language constructs

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• Communication integrity

Components in an architecture can only call each other’s methods along declared connections between ports

Components are only able to directly invoke methods of their subcomponents

ArchJava

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• Dynamic architectures

Covered by creating and connecting together a dynamically determined number of components

Connected using a connect expression at run time

A Connection pattern used to describe set of connections instantiated at run time using connect expressions

ArchJava

University of St Andrews

• Port interface

Describes a port that can be instantiated several times to communicate through different connections

ArchJava

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• Removing components and connections

No explicit way to remove components and connections

Components garbage-collected when they are no longer reachable through direct references or connections

ArchJava

University of St Andrews

ArchJava

• Communication integrity

All inter-component method calls must follow the architectural connections

Except method calls from a component to its children

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ArchJava

• Direct method calls

All direct component calls made from a sending component instance must be to the component itself or to its immediate subcomponent

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ArchJava

• Method calls through ports

a connection pattern in a component allows method calls between its immediate subcomponents through connected ports

Uses a two-part test to verify that all method calls conform to a connection pattern

Every connect expression must match a connect pattern in the component

University of St Andrews

ArchJava

• Limitations

Only applicable to a programs in a single language and running on a single JVM

Focus on communication integrity doesn’t support other architectural reasoning such as connection protocols, architectural styles, or component multiplicity

University of St Andrews

ArchJava

• Evaluation

• Can ArchJava express architecture of a real program of significant complexity?

• How difficult is it to reengineer a Java program to express its architecture explicitly in ArchJava?

• Does expressing a programs architecture in ArchJava help or hinder software evolution?

University of St Andrews

ArchJava

• Hypothesis

Hypothesis 1:

Developers have a conceptual model of their architecture that is mostly accurate, but this model may be a simplification of reality, and it is often not explicit in the code.

University of St Andrews

ArchJava

• Hypothesis 2

Programming languages that prohibit sharing data between components are too inflexible to express the natural architecture for many programs.

• Hypothesis 3

Describing an existing program’s architecture with ArchJava may involve significant restructuring if the desired architecture does not match the implementation well

University of St Andrews

ArchJava

• Hypothesis 4

Refactoring an application to expose its architecture is done most efficiently in small increments.

Hypothesis 5

• Applications can be translated into ArchJava with a modest amount of effort, and without excessive code bloat.

University of St Andrews

ArchJava

• Hypothesis 6

Expressing software architecture in ArchJava highlights refactoring opportunities by making communication protocols explicit.

• Hypothesis 7

Using separate ports and connections to distinguish different protocols and describing protocols with separate provided and required port interfaces may ease program understanding tasks.

University of St Andrews

ArchJava

• Hypothesis 8

Communication integrity in ArchJava encourages local communication and helps to reduce coupling between components

Hypothesis 9

An explicit software architecture makes it easier to identify and evolve the components involved in a change

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