cse 503 – software engineering lecture 14: introduction to software architecture rob deline
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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
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 2
What is a software architecture?
According to Google Images...
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 3
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”, ...
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 4
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”
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 5
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
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 6
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)
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 7
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.
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 8
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.
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 9
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)
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 10
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)
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 11
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.
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 12
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
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 13
Shaw and Clements taxonomy
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 14
Shaw and Clements taxonomy
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 15
Kazman et al taxonomy
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 16
Kazman et al taxonomy
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 17
Kazman et al taxonomy
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 18
Kazman et al taxonomy
UW CSE 503 ▪ Software Engineering ▪ Spring 2004 ▪ Rob DeLine 19
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
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