1. What is an Architecture?

2. An Example?
Customer
Invoice
Order
Delivery

3. Author’s Definition
The software architecture of a system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationship among them.
If you remember ONE thing,
This is the most important letter tonight

4. Structures and Views For BCK, a structure is
a set of elements AND
one or more relationship among the elements AND
defined semantics for the relationship(s)
a view is a presentation of a structure
One structure can have many views …

5. Example – two views of the “uses” structure
(uses Client Server)
(uses Client Naming)
(uses Client Message)
(uses Server Message)
(uses ServerImpl Naming)
(uses ServerImpl Server)
(uses ServerImpl Message)
Notice that the UML class diagram shows additional detail beyond the “uses” relation, including information about how one class uses another, the distinction between an interface and a concrete class, and operations of the classes. Most of this belongs more to system design than system architecture.
In this case, the uses structure has a single relation, which is called “requires the correct presence of”. I have called that relation simply “uses”; the subtleties of “requires the correct presence of” are best covered in the semantics section.

6. Three main types of views
Module
Static structure of code elements at build time
Component and Connector
Dynamics (interactions) of processes and threads at runtime
Allocation
Relationships of software elements to other resources (file systems, development teams, etc)
Bookmark Figure 2-3 on page 37
Read pages every Monday this month

7. Some commonly-viewed structures
The next 11 viewgraphs present the leaf nodes of Figure 2-3 (see Table 2.1, pp 39-40)
These are commonly-viewed structures
When documenting an architecture, you are free to define
New views of well-known structures, and/or
New structures
Just be sure to explain the elements and the semantics of the relationship(s) involved

8. Module Views Decomposition Used for: Submodule-of Shares-secret-with
Resource Allocation / Project Structure
Planning
Information Hiding
Encapsulation
Configuration Control

9. Module Views (cont.) Uses Used for: Requires-the-presence-of Subsets
Extensions
“A calls B” is a common scenario in which module A requires module B.
But there are other “requires” scenarios. For example, A might read a file written by B.

10. Module Views (cont.) Layered Used for:
Requires-the-correct-presence-of
Uses-the-services-of
Provides-abstraction-to
Used for:
Incremental Development
Portability
This is one of the most important and widely-used views currently

11. Module Views (cont.) Class Used for: Instance-of
Shares-access-methods-of
Used for:
OO design

12. Component and Connector
Client-Server
Communicates-with
Depends-upon
Used for:
Distributed Operation
Separation of Concerns
Performance Analysis
Load Balancing

13. Component and Connector (cont.)
Process
Runs-concurrently-with
May-run-concurrently-with
Excludes
Precedes
Used for:
Scheduling Analysis
Performance Analysis

14. Component and Connector (cont.)
Concurrency
Runs-on-same-logical-thread
Used for:
Analyzing Resource Contention
Where threads may fork, join, be created or killed

15. Component and Connector (cont.)
Shared Data
Produces-data
Consumes-data
Used for:
Performance Analysis
Data Integrity
Modifiability

16. Allocation Deployment Used for: Allocated-to Migrates-to
Performance Analysis
Availability Analysis
Security Analysis

17. Allocation (cont.) Implementation Used for: Stored-in
Configuration Control
Integration
Testing

18. Allocation (cont.) Work assignment Used for: Assigned-to
Project Management
Best use of expertise
Management of commonality

19. How to describe an architecture?
Many of the views can be drawn in UML
Appropriate text accompanies the diagrams
Or else you get architecture “cartoons”
An “ideal” architecture document:
5-10 pages, half pictures
Much more about UML next week (also in the book, Chapter 9.6, pp