A PPARC funded project
Review of architecture
document
Consortium meeting
Edinburgh
December 2004
Guy Rixon
AstroGrid Technical Architect
University of Cambridge
Before or after?
Architecture before implementation:
Prescriptive
We didn’t record this centrally
Contracts
Architecture after implementation:
Descriptive
Current document.
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 2
What is “architecture”
“Parts” catalogue
Compile time (e.g. classes, source-files)
Time of deployment (e.g.WARs, properties file)
Run time
Interfaces
Syntatic (e.g. WSDL)
Semantic
Parts + interfaces = relationships
Relationships + change control = contracts
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 3
Uses of descriptive architecture
“What does this bit do?”
“Where are the classes that do x?”
“How does it do y?”
“Z doesn’t work; what parts could be at fault?”
“What services does this sub-system provide?”
“If I change this, what does it affect?”
“Which bits do I install on my site?”
“You installed this on my site; what for?”
“How can I attach my s/w to AstroGrid”
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 4
Prescriptive architecture:
Contracts
<<subsystem>>
Client
Contract
<<subsystem>>
Supplier
ICD
Behaviour
One contract per major interface
Contracts have version control
Subsystems document their contracts
Developers may not merge code that breaks contracts
Need to record a new contract version first.
Intelligibility of contract tracks cohesion, coupling
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 5
Architecture: for whom?
Mainly for engineers
AstroGrid developers
External partners
Some use to service providers
“Why am I deploying this part?”
“What other parts support this part?”
Passing interest to end users
Because open source.
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 6
What the architecture doc. is not
The user manual
The science requirements
The analysis of requirements
Could be stored as appendix to architecture
The project history
Lists of technical decisions could be part of the
architecture. Q.v Brooks, MM-M.
Therefore, not the best document for some
readers.
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 7
Current architecture document (1)
Represents the system at the end of Itn6.
As-built description
No prescriptive role…
…therefore no contracts
Reverse engineered
From AstroGrid’s Maven-project structure + live
tests
Therefore not necessarily accurate…
…therefore this review.
Preparing to do a major revision for end Itn7.
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 8
Current architecture document (2)
Technical!
Based on UML model of system
Built in Together Control Centre
Published on the web:
http://astrogrid.ast.cam.ac.uk/architecture-itn6/
Most pages generated by TCC from model
A few hand-written essays
General introduction
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 9
Current architecture document (3)
Known problems:
Missing essays
No description of the portal
TCC-generated pages unwholesome
Some broken links to external pages (ex Maven)
Incomplete mapping of classes in model to Maven
projects.
Incomplete list of use cases
Doesn’t refer back to use cases ex AstroGrid
science cases
Not well integrated with CVS control.
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 10
Challenges in documenting
The architecture is not simple.
Coupling is quite high
Cohesion is quite low (in some areas)
False “information scent”
Javadocs:
Good to acceptable at class level
Not much at package level
Portal:
Code documentation lacking
Understanding by experiment only possible when the
system works
Together Control Centre
It bites!
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 11
Goals for review groups
Is the overall form of the architecture
description acceptable?
If not, would it be acceptable if more complete?
Is the description accurate?
Where does it misrepresent the Itn6 system?
What has changed since Itn6?
Is the architecture itself “wrong”?
What can most usefully be added to the
description?
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 12
Break-out groups
AG “presentation” team
AG “data” team
Visitors and partners
Rooms:
Newhaven room (here)
Deane room (reception floor)
Open area (floor below reception)
Report back after lunch
10 – 15 minute summary from each group, please.
Further notes welcome by email to
gtr@ast.cam.ac.uk
2004-12-14
AstroGrid consortium meeting 2004, Edinburgh
Slide 13