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Software Architecture
ASE
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Dimensions of software complexity
Higher technical complexity - Embedded, real-time, distributed, fault-tolerant - Custom, unprecedented, architecture reengineering - High performance
Lower technical complexity - Mostly 4GL, or component-based - Application reengineering - Interactive performance
Highermanagement complexity - Large scale - Contractual - Many stake holders - “Projects”
Lowermanagement complexity - Small scale - Informal - Single stakeholder - “Products”
Defense MIS System
Defense Weapon SystemTelecom
Switch
CASE Tool
National Air TrafficControl System
Enterprise IS(Family of ISApplications)
CommercialCompiler
BusinessSpreadsheet
IS ApplicationDistributed Objects
(Order Entry)
Small ScientificSimulation
Large-ScaleOrganization/Entity
Simulation
An average software project: - 5-10 people - 10-15 month duration - 3-5 external interfaces - Some unknowns & risks
EmbeddedAutomotive
Software
IS ApplicationGUI/RDB
(Order Entry)
Walker Royce
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Forces in Software
Technology churn
Our enemy is complexity, and it’s our goal to kill it.Jan Baan
Performance Throughput
Capacity
Availability
Fail safe
Fault tolerance
FunctionalityCost Compatibility
Resilience
The challenge over the next 20 years will not be speed or cost or performance;it will be a question of complexity.Bill Raduchel, Chief Strategy Officer, Sun Microsystems
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The domain of architecting
ArchitectureQualities
Process
Architecture Representation
The “what” The “why”
The “how”The “who”
SystemFeatures
Architecture S/W Requirements
SystemQuality Attributes
Satisfies
Constrain
Organization
Architect
Skills
Stakeholders
Defines role
Produces
Follows
DefinesTechnology
Wojtek Kozaczynski
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We all know that ...Architecture and design are the same thing
Architecture and infrastructure are the same thing
<my favorite technology> is the architecture
A good architecture is the work of a single architect
Architecture is flat, one blueprint is enough
Architecture is just structure
System architecture precedes software architecture
Architecture cannot be measured and validated
Architecture is a Science
Architecture is an Art
Philippe Kruchten
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Architecture defined (again)
Architecture n (1555) 1: the art of science of building, specifically, the art or practice of designing and building structures and esp. habitable ones 2 a: formation or construction as or as if as the result of conscious act <the ~ of the garden> b: a unifying or coherent form or structure <the novel lacks ~>
Merriam Webster’s Collegiate Dictionary10th edition
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Architecture defined (yet again)
Software architecture encompasses the set of significant decisions about the organization of a software system selection of the structural elements and their
interfaces by which a system is composed
behavior as specified in collaborations among those elements
composition of these structural and behavioral elements into larger subsystem
architectural style that guides this organization
Mary Shaw, CMUGrady Booch,
Philippe Kruchten,Rich Reitman
Kurt Bittner, Rational
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Architecture defined (continued)
Software architecture also involves usage
functionality
performance
resilience
reuse
comprehensibility
economic and technology constraints and tradeoffs
aesthetic concerns
Mary Shaw, CMUGrady Booch,
Philippe Kruchten,Rich Reitman
Kurt Bittner, Rational
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Architectural style
An architecture style defines a family of systems in terms of a pattern of structural organization.
An architectural style defines a vocabulary of components and connector
types
a set of constraints on how they can be combined
one or more semantic models that specify how a system’s overall properties can be determined from the properties of its parts
Mary Shaw, CMU
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Architecture metamodel
Software Architecture
Software Architecture Description
Architectural view
is made of
is represented by
Architecture Design Process
produces
Form
Component
Connection
Architectural Pattern
is a
is made of
Software Architects
are actors in
Logical view
Process view
Implemen- tation view
Deployment view
Requirements
satisfies
Architectural style
has
has
has
is a
System architecture
is part of
Architecture Style guide
Constraints
constrains
constrains
Use case view
relates to
Architectural Blueprint
depicts
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Models
Models are the language of designer, in many disciplines
Models are representations of the system to-be-built or as-built
Models are vehicle for communications with various stakeholders
Visual models, blueprints
Scale
Models allow reasoning about some characteristic of the real system
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Many stakeholders, many views Architecture is many things to many different
interested parties end-user customer project manager system engineer developer architect maintainer other developers
Multidimensional reality
Multiple stakeholdersmultiple views, multiple blueprints
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Architectural view
An architectural view is a simplified description (an abstraction) of a system from a particular perspective or vantage point, covering particular concerns, and omitting entities that are not relevant to this perspective
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Architecturally significant elements
Not all design is architecture
Main “business” classes
Important mechanisms
Processors and processes
Layers and subsystems
Architectural views = slices through models
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Characteristics of a Good Architecture
Resilient
Simple
Approachable
Clear separation of concerns
Balanced distribution of responsibilities
Balances economic and technology constraints
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Representing System Architecture
Logical View
End-user Functionality
Implementation View
Programmers Software management
Process View
PerformanceScalabilityThroughput
System integrators
Deployment View
System topology Delivery, installation
Communication
System engineering
Conceptual Physical
Use Case View
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Relation Between Views
Logical view Component view
Process view
Deployment view
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How many views?
Simplified models to fit the context
Not all systems require all views:
Single processor: drop deployment view
Single process: drop process view
Very Small program: drop implementation view
Adding views:
Data view, security view
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Architecture-Centric
Models are vehicles for visualizing, specifying, constructing, and documenting architecture
The Unified Process prescribes the successive refinement of an executable architecture
time
Architecture
Inception Elaboration Construction Transition
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Unified Process structure
ManagementEnvironment
Business Modeling
Implementation
Test
Analysis & Design
Preliminary Iteration(s)
Iter.#1
PhasesProcess Workflows
Iterations
Supporting Workflows
Iter.#2
Iter.#n
Iter.#n+1
Iter.#n+2
Iter.#m
Iter.#m+1
Deployment
Configuration Mgmt
Requirements
Elaboration TransitionInception Construction
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Architecture and Iterations
Use caseModel
DesignModel
DeploymentModel
TestModel
ImplementationModel
Content
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Architectural design
Identify, select, and validate “architecturally significant” elements
Not everything is architecture Main “business” classes
Important mechanisms
Processors and processes
Layers and subsystems
Interfaces
Produce a Software Architecture Documen
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Architectural design workflow Select scenarios: criticality and risk
Identify main classes and their responsibility
Distribute behavior on classes
Structure in subsystems, layers, define interfaces
Define distribution and concurrency
Implement architectural prototype
Derive tests from use cases
Evaluate architectureIterate
Use case view
Logical view
Deployment view
Implementation view
Process view
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Sources of architecture
Theft
Method
Intuition
Classical system Unprecedented system
Theft
Method
Intuition
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Patterns
A pattern is a solution to a problem in a context
A pattern codifies specific knowledge collected from experience in a domain
All well-structured systems are full of patterns
Idioms
Design patterns
Architectural patterns
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Design patterns Creational patterns
Abstract factory Prototype
Structural patterns Adapter Bridge Proxy
Behavioral patterns Chain of responsibility Mediator Visitor
Mechanisms are the soul of an architecture
Design PatternsGamma et al
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Complex business systemReal-Life Object-oriented Systems
Soren Lauesen
SQL Database
Middle layer
GUI layer
ServiceAgent
purchase(customer, product, items)
Customer
name : StringAddress : String
save()
Customer
name : StringAddress : String
save()getName()updateName()
Customer Order Line
**
Product
**
Order Line
items : Product
getName()updateName()
Observer
update()
Order
date : Date
Product
name : Stringprice : Currency
getName()updateName()
Sales
product : Product
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Logical application architecture
RelationalDatabase
GraphicalUserInterface
RelationalDatabase
GraphicalUserInterface
BusinessObjectModel
GraphicalUserInterface
BusinessObjectModel
RelationalDatabase
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Physical application architecture
Relational Database Server(s)
Client CWWW Browser
WebServer
HTMLCGI
ASP Java
Business ObjectServices
Business ObjectEngine
Application
Business ObjectServices
Client A
Business ObjectEngine
Thinner client, thicker server
Client BApplication
Business ObjectServices
Business ObjectEngine
Business Object Server
DCOMADO/R
CORBA Beans
COMMTS
BeansETS
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Complex Internet systemThe Second Wave
Paul Dreyfus, Netscape
Client
Server
ApplicationServer
FulfillmentSystem
FinancialSystem
InventorySystem
RDBMSServer
Dynamic HTML, JavaScript, Javaplug-ins, source code enhancements
Java, C, C++, JavaScript, CGI
Java, C, C++, JavaBeans, CORBA, DCOM
Native languages
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Who are the architects?
Experience software development
domain
Pro-active, goal oriented
Leadership, authority
Architecture team balance
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Architect
Not just a top level designer Need to ensure feasibility
Not the project manager But “joined at the hip”
Not a technology expert Purpose of the system, “fit”,
Not a lone scientist Communicator
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Software architecture team charter Defining the architecture of the software Maintaining the architectural integrity of the
software Assessing technical risks related to the
software design Proposing the order and contents of the
successive iterations Consulting services Assisting marketing for future product
definition Facilitating communications between project
teams
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Architecture is making decisions
The life of a software architect is a long (and sometimes painful) succession of suboptimal decisions made partly in the dark.
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Futures
ADL: Architecture Description Languages UML, UniCon, LILEAnna, P++, LEAP, Wright,
µRapid
Standardization of concepts IEEE Working Group on Architecture
INCOSE Working Group on System Architecture
Systematic capture of architectural patterns
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References (Architecture) Len Bass, Paul Clements & Rick Kazman, Software Architecture in
Practice, Addison-Wesley, 1998.
Frank Buschmann, Régine Meunier, Hans Rohnert, Peter Sommerlad, and Michael Stahl, Pattern-Oriented Software Architecture - A System of Patterns, Wiley and Sons, 1996.
Christine Hofmeister, Robert Nord, Dilip Soni, Applied Software Architecture, Addison-Wesley 1999.
Eric Gamma, John Vlissides, Richard Helm, Ralph Johnson, Design Patterns, Addison-Wesley 1995.
Philippe Kruchten, “The 4+1 View Model of Architecture,” IEEE Software, 12 (6), November 1995, IEEE.
http://www.rational.com/support/techpapers/ieee/
Eberhardt Rechtin, Systems Architecting: Creating and Building Complex Systems, Englewood Cliffs NJ, Prentice-Hall, 1991.
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References (Architecture) Eberhardt Rechtin & Mark Maier, The Art of System
Architecting, CRC Press, 1997.
Recommended Practice for Architectural Description, Draft 2.0 of IEEE P1471, May 1998
http://www.pithecanthropus.com/~awg/
Mary Shaw, and David Garlan, Software Architecture—Perspectives on an Emerging Discipline, Upper Saddle River, NJ, Prentice-Hall, 1996.
Bernard I. Witt, F. Terry Baker, and Everett W. Merritt, Software Architecture and Design—Principles, Models, and Methods, New York NY, Van Nostrand Reinhold, 1995.
The World-wide Institute of Software Architects
http://www.wwisa.org
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References (UML) Grady Booch, James Rumbaugh, Ivar Jacobson, The Unified
Modeling Language User Guide, Addison-Wesley, 1999.
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References (Process) Barry Boehm, “A spiral model of software development and
enhancement,” IEEE Computer, May 1998.
Barry Boehm, “Anchoring the software process,” IEEE Software, July 1996.
Grady Booch, Object Solutions, Addison-Wesley, 1995.
Philippe Kruchten, “A Rational Development Process,” CrossTalk, July 1996.
http://www.rational.com/support/techpapers/devprcs/
Philippe Kruchten, The Rational Unified Process - An Introduction, Addison-Wesley, 1999.
Rational Unified Process 5.0, Rational, Cupertino, CA, 1998
Walker Royce, Software Project Management: a Unified Framework, Addison-Wesley, 1998
The Software Program Manager’s Network
http://www.spmn.com