Decomposing the system

Here we transfer the analysis model design model

During system design we have to : Define design goals Decompose the system into subsystems Select strategies:

▪ Access control▪ Sw/Hw▪ DB

1. Define design goals

2. Design initial subsystem decompositionwe can use standard architectural styles as starting point

3. Refine the subsystem decomposition to address the design goals

Here we bridge the gap between requirements specification we produced and future system

In the first two phases we focused on the functionality of the system

Here we focus on how the system will do it Processes, data structures, sw/hw

The problem with SW design is conflecting constraints!!

Client needs a residential houseWe agreed upon:

Location Size Number of rooms: 2 bed rooms, 1

kitchen, I bathroom, 1 study room, 1 dining room

Functional requirements: Kitchen should be close to dining room

and garage Bathroom should be close to bedrooms Etc

Constraints Number of rooms Distance the residents walk should be

minimum Use of daylight should be maximum

stairs

kitchen

2 bedroom bath M. bedroom

study dining

entrance

stairs

kitchen

dining bath M. bedroom

study bedroom

entrance

stairs

kitchen

dining

bath

M. bedroom

study

bedroom

en

tran

ce

We did it without knowing the furniture layout…..or the layout of each room

Floor plan is similar to software design The whole is divided into subsystems and

interfaces We take into accounts functional and non-

functional requirements Design of individual components is delayed

System design impacts implementation

It will cost a lot if it is changed later on

Once your team started development, it is expensive to change later on.

1. Design goals: what qualities that should be met

2. Software architecture: describing subsystem decomposition

1. Subsystems responsibilities2. Dependencies between them3. Subsystem mapping to hardware4. Db, access control, control flow

3. Boundary use cases: describing:--startup--shutdown--exception handling