1. Decomposing the system

3.  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

4. 1. Define design goals 2. Design initial subsystem decomposition we can use standard architectural styles as starting point 3. Refine the subsystem decomposition to address the design goals

5.  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

6.  The problem with SW design is conflecting constraints!!  Client needs a residential house  We agreed upon:  Location  Size  Number of rooms: 2 bed rooms, 1 kitchen, I bathroom, 1 study room, 1 dining room

7.  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

8. stairs kitchen 2 bedroombathM. bedroom studydining entrance

9. stairs kitchen diningbathM. bedroom studybedroom entrance

10. stairs kitchen dining bath M. bedroom study bedroom entrance

11.  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

12.  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.

13. 1. Design goals: what qualities that should be met 2. Software architecture: describing subsystem decomposition 1. Subsystems responsibilities 2. Dependencies between them 3. Subsystem mapping to hardware 4. Db, access control, control flow

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