Advances in Effective Languages for Architecture Definition

Advances in Effective Languages for Architecture Definition

David [email protected]

Bradley [email protected]

ABLE Research GroupSchool of Computer ScienceCarnegie Mellon University

Pittsburgh, PA

http://www.cs.cmu.edu/~able

mailto:[email protected]





February 7, 2001 Open Group Architecture Program, San Jose, CA

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Outline• Introduction to software architecture• Terminology of Acme and ADML• Current and ongoing Acme developments• Tool support for Acme at CMU• Current and future directions

» xArch – XML infrastructure» Liaison with UML working group


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Architecture in SystemsArchitecture:

“the underlying structure of things”• not just “what”, but “why”

Good architecture (like much good design) is:

• the result of a consistent set of principles and techniques, applied consistently through all phases of a project

• resilient in the face of (inevitable) changes• source of guidance throughout the product

lifetime• reuse of established engineering

knowledge


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Issues Addressed by Architectural Design

Gross decomposition of a system into interacting components

• typically hierarchical• using rich abstractions for component interaction

(or system “glue”)• often using common design idioms/styles

Emergent system properties• performance, throughput, latencies• reliability, security, fault tolerance, evolvability

Rationale and assignment of function to components• relates requirements and implementations

Envelope of allowed change• “load-bearing walls”, limits of scalability and adaptation• design idioms and styles


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Architectures in Development

Requirements

Code

Architecture Description Languages (ADLs) providea method for specifying software architectures

?Requirements

Code

Software Architecture


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Why ADLsADLs provide a way to model designs precisely and explicitly:

• Focus attention on essential design factors• Enable unambiguous communication• Provide a secure foundation for reasoning• Enable automated analysis

There are over a dozen ADLs in use today


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Commonalities among ADLsADLs largely agree on use of structure:

• Components: define the locus of computation» E.g.: filters, databases, objects, clients, servers

• Connectors: mediate component interactions» E.g.: procedure call, pipes, event broadcast

• Interfaces: component interface to envt.» E.g., http socket, corba/com interface

• Properties: specifications for compilation and analysis

» E.g.: signatures, pre/post conditions, RT specs


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Acme – A Generic ADLAcme was originally developed as an exchange language for architecture descriptions

• Embodies commonality between ADLs• Domain-Neutral structural descriptions• Properties for encoding semantics• Extensibility through type-system and tools

This is in contrast with other ADLs, which have “hard-wired” semanticsADML was based heavily on Acme, and so the

terminology for Acme applies to ADML


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Acme Structural Language

connector

componentsystem

role

port

attachment


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Acme PropertiesProperties provide a semantic extension mechanism to Acme

• Arbitrary attribute-value annotations• Associated with all major language

constructsDomain specific information can be captured in properties

• E.g.: protocols of interaction, performance, reliability


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Acme Representations• Hierarchical abstractions (encapsulation)• Can represent sub-architectures or “views”

System(sub-architecture)

Binding

Representation


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Architectural StylesNeed to capture domain-specific architectural elements

• For specific kinds of components, connectors • For a particular software system or enterprise

This is done through the definition of Acme families

• Defines architectural vocabulary• Defines constraints on use of that vocabulary• May define specialized visualization for tools


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Style ExampleIf we are defining a software system using a style called Pipes and Filters, then we can define types:

• Pipe – a particular kind of connector, with two roles named source and sink

• Filter – a particular kind of component, with default ports in and out

Architectures defined in this style can make use of this vocabulary


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ADMLADML (Architecture Description Markup Language) is:

• An XML encoding of architectures (as already outlined)• Being promoted by the Open Group for specification of

enterprise architectures• Originally developed at MCC

ADML adds to Acme:• Industry-standard representation (parsable by ordinary

XML parsers)• The ability to define links to objects outside the

architecture• Straightforward ability to interface with commercial

repositories, and transparent extensibilityHowever, Acme has been extended in recent years


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Armani Design ConstraintsArmani is a constraint language extension to Acme

• Based on first-order predicate logic• Augmented with architecture-specific predicates• For defining architectural element types and styles

Armani constraints specify how a design may evolve over time. Examples:

• A particular type of component can only have particular types of ports

• Property values must be within certain rangesTwo types of constraints

• Invariants must never be violated• Heuristics should be observed but may be selectively

violated


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Current ResearchMapping between multiple views

• Expresses correspondence between multiple views of an architecture

Runtime architectural events• Dynamic events in an architectural context

Repair strategies• Architectural modifications that can occur at

runtime when constraints fail


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Acme Tools at CMU

AcmeLib – A foundation for building tools

AcmeStudio

Armani constraintchecking

Performance analysis

AcmeADMLxArchMeta H…


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AcmeStudioGraphical design environment for Acme

• Supports development and analysis of architectural descriptions

Customizable for different architectural styles• Domain-specific design vocabulary captured in types and

families• Graphical depictions of architecture based on style• Style-specific analysis tools

Interfaces to other design tools• Armani constraint checker• Various analysis tools (e.g., performance analysis)• Exports ADML (import planned)


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AcmeLibAcmeLib is a library supporting Acme

• Defines an object library for creating and manipulating architectural representations in Acme

• Provides parser/unparser to import/export Acme descriptions

• Available in C++ and JavaAcmeLib is a common data structure that can be used as the foundation for various architectural tools


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xArch A core XML representation for architecture structure

• Simpler than ADML/Acme – just hierarchical component-connector graphs

• Defined using an XML Schema

For use within DARPA/DASADA Program• For experimentation and future extension• Developed in collaboration with CMU

(Garlan/Schmerl), UCI (van der Hoek/Taylor) and TeKnowledge (Wile)


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xArch ExtensionsSeveral groups are extending xArch

• CMU: ADML/Acme extension» Plans to marry xArch and ADML» Layered approach» Initially: Types, Properties, Families» Later: Constraints, mappings, events

• UCI extensions» Currently: Types, Versions and variants,

Implementation


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xArch, Acme, ADML

xArch

ADML*

ADML+

Core-Acme

Acme

Acme+Armani

structure

properties, types,families

constraints

events, versions, patterns

XML Acme Contents


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UMLUML story is needed

• To support integration of software architecture with standard UML tools and notations

Architectures and UML used for different phases of a design lifecycle

• Many ways to encode architectures in UML• UML experts may assign different semantics

depending on which strategy is used


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Acme and UMLTwo paths for integrating Acme and UML

• Provide translators between Acme and UML• Collaboration with OMG to include architectural

concepts in UML 2.0» Proposal for UML 2.0 extensions due out soon

– Includes extensions to UML metamodel for architectural modeling

– Taking Acme as a starting point

Both paths are being pursued at CMU


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Summary• Acme and ADML distill elements common to

other ADLs• Research is continuing in software architecture

on several fronts• There is a need to reconcile different XML

encodings• There is ongoing work in understanding and

codifying the relationship between architectures and UML

• For more information:» http://www.cs.cmu.edu/~able

Advances in Effective Languages for Architecture Definition

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