1. A PPARC funded project Review of architecture document Consortium meeting Edinburgh December 2004 Guy Rixon AstroGrid Technical Architect University of Cambridge

2. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 2 Before or after? Architecture before implementation: Prescriptive We didn’t record this centrally Contracts Architecture after implementation: Descriptive Current document.

3. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 3 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

4. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 4 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”

5. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 5 Prescriptive architecture: Contracts 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 > Client > Supplier Contract ICDBehaviour

6. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 6 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.

7. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 7 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.

8. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 8 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.

9. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 9 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

10. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 10 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.

11. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 11 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!

12. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 12 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?

13. 2004-12-14AstroGrid consortium meeting 2004, Edinburgh Slide 13 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 gtr@ast.cam.ac.uk