COMP 6471
Software Design Methodologies
Winter 2006
Dr Greg Butler
http://www.cs.concordia.ca/~gregb/home/comp647-w2006.html
The CU WME Design Case Study
Concordia University Work Management Environment (CU
WME) provides support for an organisation of people
who produce and publish documents
Components:
•
•
•
•
•
User Management
File Management
Change Management
Activity Management
Collaborative Publication
• Project Management
The CU WME Design Case Study
How do components distribute responsibilities and
what are their dependencies?
Separate mechanisms from policy.
Components:
•
•
•
•
•
User Management
File Management
Change Management
Activity Management
Collaborative Publication
• Project Management
The CU WME Design Case Study
How do components distribute responsibilities?
• User Management: manage users, roles, rights
• File Management: provide file/directories, operations for
access, back-up. Access control?
• Change Management: change of what?, provide
operations, how much policy?
• Activity Management: monitor, log. How much policy of
control? What mechanisms for control?
• Collaborative Publication=Document management:
mechanisms on documents, concept of document, what
is difference between file mgmt vs doc mgmt?
• Project Management: mechanisms for project definition,
policy for ….
The CU WME Design Case Study
What are their dependencies?
•
•
•
•
User Management depends on …FM?
File Management depends on …UM?
Change Management depends on FM?
Activity Management depends on FM,
UM?
• Collaborative Publication depends on UM,
FM, CM, AM
• Project Management depends on ???
The CU WME Design Case Study
Separate mechanisms from policy.
Which set policy, which provide implementation to enforce
policy, which provide basic mechanisms?
Components:
•
•
•
•
•
User Management
File Management
Change Management
Activity Management
Collaborative Publication
• Project Management
CU WME – User Management
Responsibility:?
RBAC (Role Based Access Control) concepts
User
Role (enumerated list)
Operation (eg, read, write, …)
Object (= Resource, ie Document/File)
Permission of Role to perform an Operation on Object
RBAC1 allows role hierarchy (DAG)
RBAC2 adds constraint condition (ie lock exists on
Object) to modify permissions
CU WME – User Management
Responsibility:?
Does not need to define specific roles for the
system, not Operations, nor Objects: these
might be requirements from other Components.
Eg, role of project management from PM (C6)
Eg, operation read for Object file(“…”) from FM
(C2)
CU WME – File Management
Responsibility:?
Unix File System
File is stream of bytes to provide uniform abstraction
Directory hierarchy mixes files/directories/links as
entries
File identified by pathname (cf URI)
Unix permissions (rwx) for roles (user, group, other)
Does CUWME FM need its own access control?
Who provides storage for UM?
How to manage copies of files? Versions of files?
CU WME – File Management
Responsibility:?
Back-up in FM
What are mechanisms
What are policies for back-up, where are they set
What storage (ie files) are needed for back-up?
Are these managed by FM?
Do these have back-up needs?
File replication in distributed system
Same file exists in different location
What does “same” mean here? Implications for file
operations are …
How is this managed by FM?
CU WME – File Management
Responsibility:?
Are files atomic?
How does FM relate to Change Mgmt and
Document Mgmt?
Does FM set policy (ie define) how a document is
stored by FM? How a change is stored in FM?
How a change is named?
Do we back-up files or documents? If both, how is
doc back-up related to file back-up?
Is a back-up a change, activity, copy, version, …
CU WME – Change Management
Responsibility:?
Concurrent Versions System (CVS)
Is version control management system
Versions of what? …for CVS source code files, binaries,
documentation
Check-out/check-in to manage concurrent access
Version branches … which can be merged later
(manually)
Tracks versions, not changes
Storing deltas (ie changes) is an implementation optimization
CU WME – Change Management
Responsibility:?
Version of file or document or resource or …?
Dependency on FM? for storage
Which operations create a new “version”?
Which do not?
How do permissions on X carry over to
permissions on version of X? or copy of X …
Who sets this policy? Where?
CU WME – Change Management
Responsibility:?
Do change management of files
This is basic building block.
Do change management of documents
Remember documents are composite/recursive.
CU WME – Activity Management
Responsibility:?
Look at basic concepts of web session or DB
transaction or Command pattern
Session is a sequence of activities by a user (from
beginning to end)
Activity is execution of an operation (C1) or command
(GOF) or activity (C6)
AM (C4) records/logs activities with info
Session, activity, user, role, …
Who is responsible for session creation?
Collaborate with UM (C1) to ensure user has
permission for the activity (operation).
CU WME – Activity Management
Responsibility:?
Can a user have many sessions at once?
Where are command objects created? Executed?
Recorded?
Does FM supply storage for log?
How do operations which create versions
communicate to CM (C3) that a version has
been created?
CU WME – Activity Management
Responsibility:?
Remember that AM provides mechanisms, not
policies.
CU WME – Collaborative Publication
Responsibility:?
…is this just Document Management?
It should provide mechanisms, not policy.
However, it must provide mechanisms that
support the enforcement of policy, eg
concurrency.
Does this component need to define specific roles
and permissions? Or can this be done
separately using UM (C1)?
CU WME – Collaborative Publication
Responsibility:?
Think of a document as an XML document, ie
composite.
How do you capture dependencies between a
document and its parts? And the files? And its
build process? [ie, compare document
publication with software development]
You need back-up and versions of documents: can
you simply rely on FM back-up facility?
CU WME – Collaborative Publication
Responsibility:?
I do not know of any good CP/DM(C5) system to
refer you to as an example.
“groupware” tends to focus on calendars, chat,
notification rather than documents themselves.
“issue tracking” tends to just look at issues and
their resolution, but not document changes (or
source code changes)
OpenText Livelink is a Canadian example, but it
does everything in CU WME and more
Lotus Domino from IBM is also of interest
CU WME – Project Management
Responsibility:?
Keep the scope simple.
This is the place for policy – maybe not the only place.
Define project:
Sequence of activities, resources (ie roles) required, and schedule
(in timeunits of duration).
Create project:
Set start date, assign users to roles.
Monitor project progress:
Collaborate with UM (C1) so that user session is associated with a
project and role: assigned activities are RBAC “operations” on
certain “objects”.
Collaborate with AM (C4) to check whether activities are done.
CU WME – Project Management
Responsibility:?
Composite pattern for project? Or for process?
So a project can be a sequence of activities and/or
subprojects. Allows easier definition of projects.
Set/enforce policy? User can only work on
assigned projects? User can only do scheduled
activities?
CU WME – Project Management
Responsibility:?
Again, difficult to find a simple example for you.
Java open source projects include “Ganttproject”
(a MS Project in Java) and “teamwork”.
OpenText Livelink has project management.
Fig. 13.3
UI
Domain
Swing
Sales
Web
UI
UI::Swing
UI::Web
Swing
Web
Domain::Sales
Domain
Sales
Important Concepts
Model
• Abstraction hiding (unimportant) details
• Eg, cover of Larman’s book
GRASP Principle
• for assigning responsibility
Design pattern
• Solution to design problem in context
• Eg, Command pattern
Responsibility-Driven Design (RDD)
• Detailed object design is usually done
from the point of view of the metaphor of:
– Objects have responsibilities
– Objects collaborate
• Responsibilities are an abstraction.
– The responsibility for persistence.
• Large-grained responsibility.
– The responsibility for the sales tax calculation.
• More fine-grained responsibility.
The 9 GRASP Principles
1.
2.
3.
4.
5.
6.
7.
8.
9.
Creator
Expert
Controller
Low Coupling
High Cohesion
Polymorphism
Pure Fabrication
Indirection
Protected Variations
Command Pattern
• You have commands that need to be
– executed,
– undone, or
– queued
• Command design pattern separates
– Receiver from Invoker from Commands
• All commands derive from Command and
implement do(), undo(), and redo()
• Also allows recording history, replay