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Software Architecture andSoftware Architecture andSoftware Configuration Management Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
RWTH Aachen, Germany/
NTNU Trondheim, Norway
SCM 10
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Software process (simplified view)Software process (simplified view)
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requirements engineering
programming-in-the-large
programming-in-the-small
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
DefinitionsDefinitions
An architecture is the set of significant decisions about theorganization of a software system, the selection of the structuralelements and their interfaces by which the system is composed,together with their behavior as specified in the collaborations amongthose elements, the composition of these structural and behavioralelements into progressively larger subsystems, and the architecturalstyle that guides this organization.[Booch, Rumbaugh, Jacobson 1999]
Configuration management is the process of identifyingand defining the items in the system, controlling the changesto these items throughout their life cycle, recording and reportingthe status of items and change requests, and verifying the completeness and correctness of items.[IEEE 1983]
Or: the discipline of controlling the evolution of complex software systems[Tichy 1988]
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Questions/goalsQuestions/goals
Investigate the borderline between software architecture and SCM» Product space» Version space
Investigate the division of labor between ADL tools and SCM systems» To what extent may an ADL tool rely on services provided by
an SCM system?» To what extent should an SCM system already incorporate
support for software architecture?» From the perspective of an ADL tool builder:
What are the requirements to SCM services?
In what respects do current SCM systems not (or not adequately) address these requirements?
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Architectural Description Languages (ADLs)Architectural Description Languages (ADLs)
Architecture Modeling Features
Components» Interface, Types, Semantics,
Constraints, Evolution
Connectors» Interface, Types, Semantics,
Constraints, Evolution
Architectural Configurations» Understandability,
Compositionality, Heterogeneity, Constraints, Refinement and Traceability, Scalability, Evolution, Dynamism
Tool Support
Active Specification
Multiple Views
Analysis
Refinement
Code Generation
Dynamism
[Medvidovic and Taylor 1997]
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
ADL Examples (1): UMLADL Examples (1): UML
SubRepresentation
getContentPane()
ReprElement
1..*1..*
ViewWindowManagerviewWindowNames : ArrayviewWindowDescriptions : HashMapviewWindowImplementations : HashMap
openViewWindow()removeViewWindow()getViewWindowNames()getViewWindowDescription()retrieveInstalledViews()
GraphFilter(from fi l ters)
ViewviewName : String
getName()incrementalUpdate()completeUpdate()closed()attach()detach()
ViewWindow
open()close()attachView()detachView()
0..*-openViewWindows 0..*
1..*
-openViews
1..*
Unparser
incrementalUpdate()completeUpdate()
<<Interface>>
#unparser
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
ADL Examples (2): Acme [Garlan et al. 1997]ADL Examples (2): Acme [Garlan et al. 1997]
component
connector configuration
representationvariant
representationvariant
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
ADL Examples (3): Wright [Allan and Garlan 1997]ADL Examples (3): Wright [Allan and Garlan 1997]
component Client =port Request = ......
component Server =port Provide = ......
connector Service = role Client = request!x → result?y → Client ∏ √role Server = invoke?x → return!y → Server √glue = Client.request?x → Server.invoke!x
→ Server.return?y → Client.result!y → glue
√
specificationof semantics
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
ADL Examples (4): Ménage [van der Hoek et al. 1997]ADL Examples (4): Ménage [van der Hoek et al. 1997]
revision
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
ADL Examples (4): Ménage [van der Hoek et al. 1997]ADL Examples (4): Ménage [van der Hoek et al. 1997]
optionalcomponent
variantvariant
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Software configuration managementSoftware configuration management
Deals with items = software objects and their relationships,objects are typed: source/derived, atomic/composite, etc.
Composition of these elements into configurations
Version control (evolution of objects, relationships, and configurations)
Representation of software architectures» Make files» System models dealing with
design objects
arbitrary software objects
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
System models for design objects (1):System models for design objects (1):Adele I [Estublier 1984]Adele I [Estublier 1984]
manual m2_i2_v2selimp
m4-i2-v1.05selcond
>*(syst = unix)>* (connect = pipe)
seldef>* (type = debug)
attributestype = debugsyst = unixauthor = Jimstate = experimentaldate = 84_05_13
end
built-insystem
modelinglanguage
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
System models for design objects (2):System models for design objects (2): Adele II [Estublier 1994] Adele II [Estublier 1994]
type Interface is Object;common
system : {unix, hp, vms};graphics : {x11, open_win};
modifiablebelong-to : Conf;bug-reports : set_of Document
immutableheader : File;realization : versioned
Realization;end;
user-defined
versionedobjecttype
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
System models for arbitrary software objects:System models for arbitrary software objects:PCL [Tryggeseth et al. 1995]PCL [Tryggeseth et al. 1995]
family fooattributes os : {Unix, VMS, DOS};...endparts
root ⇒ main;
files ⇒ if os = Unix then unix_fselsif os = VMS then vms_fselse dos_fs;
...end
end
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Comparison of software architecture and SCMComparison of software architecture and SCM
software architecture SCM
coverage programming-in-the-large(high-level design)
whole lifecycle
softwareobjects
components, modules,classes, ...
all kinds of software objects
relationships inheritance, import, portconnections, ...
all kinds of relationships
semantic level high (syntactic or semanticconsistency)
fairly low
granularity overall organization, butalso detailed interface
descriptions
overall organization(software objects as black
boxes)versions variants variants and revisions
version selection usually hard-wired rule-based
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 1 Architectural design vs. the whole lifecycleThesis 1 Architectural design vs. the whole lifecycle
Software architecture and SCM overlap since they both dealwith the overall organization of a software system. However,while software architecture refers to programming-in-the-large,SCM addresses the whole software lifecycle.
soft
war
e co
nfig
ura
tion
man
agem
ent
qu
alit y
assu
ran
ce
requirements engineering
programming-in-the-large
programming-in-the-small
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 2 Tool integration - bottom-up or top-downThesis 2 Tool integration - bottom-up or top-down
The relation between software architecture and SCM can bestudied under different assumptions concerning tool integration.It makes a big difference whether we assume bottom-up ortop-down integration.
architecturaldesign tool 1
architecturaldesign tool m
SCM system 1
SCM system n
... ...
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 3 Different system description languagesThesis 3 Different system description languages
Since there are many architectural description languageswith different syntax and semantics, an SCM system must notprescribe a specific language for describing software architectures.In contrast, the software architecture description has to be handled like any other document.
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 4 Unavoidable redundancy in system descriptionsThesis 4 Unavoidable redundancy in system descriptions
Under the constraints of bottom-up integration, there is no hopeto unify software architectures and software configurations in thesense that only a single, integrated description needs to bemaintained. A certain amount of redundancy is therefore inevitable.
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 5 Planned evolution is easyThesis 5 Planned evolution is easy
Architectural design deals with architectural evolution at asemantic level. In particular, variants can be represented withinthe software architecture description (as realization variants,subclasses, or instances of generic modules). In the way, plannedevolution may be taken care of.
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 6 Unplanned evolution is hardThesis 6 Unplanned evolution is hard
SCM offers general version control services for all kinds ofapplications. These address not only variants, but also revisions.Version control is performed at a fairly low semantic level. TheSCM system deals with versioning of the architecture, coveringin particular unplanned evolution.
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Thesis 7 Evolution at different abstraction levelsThesis 7 Evolution at different abstraction levels
Altogether, the evolution of software architectures has to be dealtwith at two levels: “structured” version control within the architecture (planned changes) and “unstructured” version controlof the architecture (unplanned changes). These two levelscomplement each other and cannot be unified easily.
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Summary: Spectrum of modeling alternativesSummary: Spectrum of modeling alternatives
Standard design languages, such as UML, SDL, etc.
Make files (composition, dependencies, derivation),can be partly extracted from source code
Simple system modeling languages from SCM systems:Adele, PCL, DSEE, etc.general objects/relationships, version support
Richer architectural languages:Acme, Wright, Ménage, etc.design objects, relationships, rich semantics
SCM 10
Software Architecture and Software Configuration Management
Bernhard Westfechtel and Reidar Conradi
Interplay between software architecture and SCMInterplay between software architecture and SCM
Redundancy cannot be avoided» How to keep consistency between architectural
configurations and SCM configurations?» How to select the appropriate level of granularity?
Potential problems of current SCM systems from the perspective of ADL tool builders» SCM version model does not match the needs of an ADL
tool» SCM version control is performed at a low semantic level» SCM system enforces its own ADL
Desired features of SCM systems:» Customizable support for representing design objects and
their relationships» More flexible version model
Raise the semantic level of version and configuration control