CSE 503 – Software Engineering Lecture 14: Introduction to software architecture Rob DeLine

UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 1

CSE 503 – Software Engineering

Lecture 14: Introduction to software architecture

Rob DeLine

12 May 2004


What is a software architecture?

According to Google Images...


What do these figures contain?

Components (boxes) Places where computation takes place Places where data is stored Box shapes discriminate component type

Connections (lines) Some kind of interaction among components Often binary, sometimes n-ary Line attributes discriminate connection types

Composition (grouping, backgrounds, fences) Show commonality, boundaries

Often accompanied by descriptive jargon “pipe and filter”, “client/server”, “object-oriented”,

“publish/subscribe”, “layered”, “microkernel”, “web services”, ...


Carving out a new level of abstraction

In the early age of programming languages...

sum := 0;i := 0;while (i < 10) { sum := sum +

i; i := i + 1;}return;

10: stconst r0, 011: stconst r1, 012: stconst r2,

1013: sub r2,r0,r414: bz r4, 1815: add r1,r0,r116: incr r017: br 1218: ret

sum := 0

i := 0

i <= 10

sum := sum + i;

i := i + 1;

return

T

F

no control abstractions

semi-formal notations and jargon

precise notations and disciplines

“structured programming”


Architecture as a new abstraction

Researchers are carving out a higher-level abstraction

architectural description languages (ADLs)

s = socket(...);bind(s, ...);listen(s, ...);while (true) { x =

accept(s, ...); receive(x, ...); close(x);}

no interaction abstractions

semi-formal notations and jargon

precise notations and disciplines

pattern languages and other guidance

classifications


Architectural description languages

In the 90s, researchers created many architectural notations grew out of module interconnection languages (1975) focus on recording system structure (typically static

structure) different goals, but many shared concepts

Common concepts Components Connectors (common disagreement: aren’t these just

components?) Compositions (combinations of elements to form new

elements) Architecture style (constraints on elements and their

composition)


UniCon

Focus on encapsulating complex construction rules Editor lets you drag-and-drop elements and hook them up

Given a system description, UniCon’s compiler produceslow-level interaction codebuild instructions (makefile) that invokes

needed tools

Shaw, DeLine, Klein, Ross, Young and Zelesnik, “Abstractions for software architectures and tools to support them”, Trans. on Soft. Eng. 21(4):314-335.


Wright

Focus on making interaction formal Components interact through ports Connectors interact through roles Attachments are made by binding ports to roles Ports and roles are formally defined as CSP processes Port/role compatibility is a process refinement check

Since we studied process calculi, let’s look in more detail...

Allen and Garlan, “Formalizing architectural connection”, ICSE ’94.


Wright component description

Split is a “tee” filter

component Split =port In = read?x -> In [] read-eof close port Left, Right = write!x Out ┌┐close comp spec =

let Close = In.close Left.close Right.close in Close []

In.read?x Left.write!x (Close [] In.read?x Right.write!x

computation)


Wright connector description

A pipe is a queue of text

connector Pipe =role Writer = write!x Writer ┌┐close role Reader = let ExitOnly = close in let DoRead = (read?x Reader [] read-eof ExitOnly)in DoRead ExitOnly

glue = let ReadOnly = Reader.read!y ReadOnly [] Reader.read-eof Reader.close [] Reader.close

in let WriteOnly = Writer.write?x WriteOnly [] Writer.close

in Writer.write?x glue [] Reader.read!y glue [] Writer.close ReadOnly [] Reader.close WriteOnly

spec Reader.readi!y . Writer.writej?x . i=j x=y

Reader.read-eof (Writer.close #Reader.read = #Writer.write)


Wright system description

A system composes components and connectors

system Capitalizecomponent Split = ...connector Pipe = ......

instancessplit: Split; p1, p2: Pipe;

attachmentssplit.Left as p1.Writer;upper.In as p1.Reader;split.Right as p2.Writer;lower.In as p2.Reader;...

end Capitalize.


Classifying aspects of architecture

Taxonomies and other classifications Gather known examples into rigorous, but not formal,

structure Often a good first step toward theory Important precedents in biology, chemistry

Examples Shaw and Clements, “A field guide to boxology: Preliminary

classification of architectural styles for software systems,” Compsac ’97

Kazman, Clements, Abowd, and Bass, “Classifying architectural elements as a foundation for mechanism matching,” Compsac ’97

DeLine, “A catalog of techniques for resolving packaging mismatch”, Symp. on Software Reusability 1999

Mehta, Medvidovic, and Phadke, “Towards a taxonomy of software connectors”, ICSE 2000


Shaw and Clements taxonomy


Kazman et al taxonomy


Guidance

Researchers are recording what experts know about arch. Given a problem, how do I pick an architecture?

Lane, “Studying software architecture through design spaces and rules,” Tech Report CMU-CS-90-175

Given a set of extrafunctional requirements, how do I pick an arch.?

Kazman, Bass, Abowd, Webb, “SAAM: A method for analyzing the properties of software architectures,” ICSE ’94

Given a set of attacks and security tools, which is most cost effective?

Butler, “Security attribute evaluation method: a cost-benefit approach”, ICSE ’02

Important case: pattern languages Catalogue of problem/solution pairs Next Mon: A quick tour of Gamma &al’s pattern language Next Wed: A quick tour of different architectural styles

CSE 503 – Software Engineering Lecture 14: Introduction to software architecture Rob DeLine

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