Architectural Design Resolutio n

1. Architectural Design Resolution Chapter 10

2. Architectural Design Resolution Architectural Design Process Develop Architectural Design Alternatives Analyzed SRS Evaluate Architectural Alternatives Select Architectural Resolution [else ] [selected ] Finalize Software Architectural Document SAD

3. Various Alternatives to Generating Architectural Design from scratch • Develop Functional Components • Based on transforming SRS functional and data requirements • Determine/Modify Components Based on “Quality Attributes”: maintainability, reusability, performance, availability & security (non-functional attributes) • Based on transformingnon-functional SRS requirements • Modify Existing Architecture (for follow-on releases) • Based on existing architecture as a starting point and transforming it to satisfy the new system • Elaborate an Architecture Style (chapter 15) • Based on an existing architectural style and elaborate on that style • Transform a Conceptual Model (chapter 11-Detailed Design) • Based on viewing the SRS problem description as a solution description and transforming that to fit the new system

4. Architectural Design (team or individual activity?) • In software engineering, many activities are performed as a team effort --- for • Productivity • Quality • Morale and General Acceptance • But for Architectural Design: • Better done as an individual first • Bring together all the individual architectural designsuggestions • Evaluate the alternatives

5. Determine Functional Components(Using the “AquaLush Irrigation System” Example in textbook – p.82 and p.164) AquaLush Product Vision: The AquaLush Irrigation system will use soil moisture sensorsto control irrigation, thus saving money for customers and making better use of water resources. • AquaLush Major Product Features (from requirements): • - Monitor water usage and limit usage (by moisture level) to amounts set by users • - Allow users to specify times when irrigation occurs • - Be operated from a simple central control panel • - Have a web-based simulator • - Allow users to monitor parts and schedule repairs What would you list as major “functional components ?” (e.g.) 1. user interface to initialize, set-up, monitor and control the irrigation system 2. sensor inputs processing 3. water irrigation control 4. web-based simulator 5. parts monitor and repair

6. Determining Functional Components from SRS(page 289 – 291 textbook solution) 1. configure the program at startup 2. controlling irrigation (manually and automatically) 3. providing a user interface 4. allowing users to monitor and repair system From page 289 <<component>> User Interface From page 180 <<component>> Irrigation Control <<component>> Monitor and Repair <<component>> Startup Do the functional components and the relation “lines” make sense to you? (Should there be a line between User Interface and Startup ?)

7. Determining Functional Components(page 289 – 291 textbook solution for product) 1. configure the program at startup 2. controlling irrigation (manually and automatically) 3. providing a user interface 4. allowing users to monitor and repair system Note that Monitor and Repair component can use the Data Store to communicate with Irrigation Control component, without a line between them. <<component>> User Interface <<component>> Monitor and Repair <<component>> Irrigation Control <<read & write>> << read & write >> <<component>> Startup AquaLush Parts Status <<startup reads config. data>> AquaLush Configuration How initialized?

8. Component Responsibilities • There needs to be some description of each component’s responsibilities: • User Interface: interacts with control panel hardware and implements control panel interface; obtains data from Monitor and Repair ------- • Monitor and Repair: Obtains data from Parts Status to pass on to ------ • Irrigation Control: Controls valve, reads sensors; reads clock; implements irrigation cycles; --- • Startup: reads the configuration data of valves, zones, etc. and sends them to Irrigation Control & (alternatively also include Monitor Repair) ---- • Parts Status: a database that keeps track of all failed and repaired parts, etc. • Configuration: a database of all the installed parts of valves, sensors, etc. of the customer’s Aqualush system

9. Determining Functional Components(page 293 textbook - for adding web-simulator) <<component>> Simulating Valves and sensors <<component>> Simulating User interaction <<component>> Monitor and Repair <<component>> Irrigation Control <<read & write>> << read & write >> <<component>> Startup AquaLush Parts Status <<startup reads config. data>> AquaLush Configuration Same initialization problem?

10. Determining Components based on“non-Functional” or “Quality” attributes • AquaLush has the following non-functional (NF) requirements: • Reusability : design must be used in the product, web-simulator, and future versions • Hardware adaptability: design should consider adaptability to multiple valve types, sensor types, keypads, and screen display types • Reliability: must not fail “often” in normal usage • Modifiability: accommodate future changes in irrigation strategy (formula) Note that reliability of not failing “often” is a nebulous and subjective statement

11. NF: Reusability Attribute • Requires components to be cohesive and loosely coupled so that they can be reused. • Consider each component for these: • Would you subdivide User Interface/interaction component into several subcomponents (interface to Irrigation Control and to Monitor and Repair separately)? • Would you separate out Irrigation Control component into a) manual and b) auto subcomponents? - etc. Irrigation Control Manual control automatic control

12. NF : Hardware Adaptability & Modifiability • Requires the component to have device adaptability; also implies • separate cohesive subcomponents • low coupling subcomponents, each representing different device • hides the device specific internals and keeps the interface unchanging • In AquaLush, the Irrigation Control has interfaces to multiple devices. • In AquaLush, Monitor and Repair component and Startup component have interface to a data-store Virtual Device Interface May change algorithm based on different sensors valve display Screen buttons How would you design a single read/write “interface” ? sensor keypad Everything inside the Device Interface components are device dependent, but hidden from outside; all interfaces to outside of the component should stay stable

13. NF: Reliability and other components • Reliability may be argued many ways: • Small cohesive module is by definition more reliable • Add user interface to control irrigation both manually and automatically AND also have direct control of the devices User Interface Emergency Control Irrigation Control manual auto Agree with all the interaction lines ? Do we need a new component ? Virtual Device Interface valve Sensor display keypad Screen buttons Designer’s view of providing reliability ---- “ not fail often in normal usage”

14. Design Alternatives • Design alternatives are good to have and can improve the design: • Generate and document these alternatives as the design is getting formulated • Combine some of parts of the generated design alternatives from: • Functional Components • Non-functional Components • Try to alter and fit to an existing Design Style, if applicable

15. Architectural Design Resolution Architectural Design Process Develop Architectural Design Alternatives Analyzed SRS Evaluate Architectural Alternatives Select Architectural Resolution [else ] [selected ] Finalize Software Architectural Document SAD

16. Evaluating Architecture Alternatives • What does one look at when evaluating architecture? • Would the architecture result in a system that will satisfy: • Functionalrequirements • “Quality” (non-functional) requirements • Maintainability • Reusability • Performance • Availability • Reliability • Security • Would the architecture result in a system that will: • Have “great” user experience or user interface • Delight the customer and the users We cannottell what will happen since the architecture is not code, we can only “guess” whether the architecture will most likely meet the above conditions

17. An Architecture Evaluating Technique • Utilize a “profile,” which is a set of scenarios generated to fit the characteristics of interest. (e.g.) • Usage profile is a set of scenarios that describe the user requirements (sometimes known as regular “business” workflow) • Reliability profile is a set of scenarios that portrays the non-functional requirement of how a system behavesunder adverse situations • Performance profile is a set of scenarios that portray the non-functional requirements of how a system behaves undertime limit constraints or capacity limit constraints • etc. • Each architecture alternative is evaluated by going through thescenarios in the profile and assessing whether the architecture, if implemented, would satisfy the profile.

18. Developing Profiles with “utility tree” • A utility tree is a tree where each sub-tree is a “profile” and the leaves of the sub-tree are the scenarios for that profile 1. The profiles are generated, using SRS and some brainstorming 2. The scenarios within each profile are also developed using SRS, ‘team’ brainstorming, and prioritizations. 3. Within each profile, keep the number of scenarios from 3 to 10 4. Each scenario should include: - initial state - activity flow involving actors and the product - post activity state * * think of special circumstances and non-traditional scenarios, too Utility tree Functionalities Irrigation control (automatic) Irrigation control (manual) Maintenance repair Hardware adaptability Valve type modification Adding new valve types

19. Another Architecture Evaluating Technique • Build a “prototype”of part of or of the complete software product to evaluate certain aspects (functional and non-functional) of the product. • Advantages: • Can provide measurements • Can provide experiential feedback • Disadvantages: • Prototypes take resources • Prototypes take time Much of the prototyping and profiling techniques are aimed at evaluating the architecture against the “basic” design principles (discussed earlier) : - feasibility, - adequacy, - economy, and - changeability

20. Selecting Alternatives • How do we select the architecture from the various alternatives ? • Evaluate the Pros and Cons of each of the alternatives • By Number of pros and cons • By Weights of pros and cons • Multi-dimensional analysis table (p. 306 of text): • A Column of scenarios • Weight for each scenario (use normalized weight so each is a fraction of the total and the total is 1) • A Column for each architectural alternative • Rate all the scenarios for that alternative ( e.g. 1-5) • Score the scenario by multiplying the scenario weight and the rate • Sum the scores for that alternative • Compare the total score for each of the architectural alternatives

21. Architectural Design Resolution Architectural Design Process Develop Architectural Design Alternatives Analyzed SRS Evaluate Architectural Alternatives Select Architectural Resolution [else ] [selected ] Finalize Software Architectural Document SAD

22. Finalizing The Architectural Design • This step ensures that the selected architecture satisfies the various functional and non-functional requirements (and possibly may delight the users) and is clearly documented. • Architectural design satisfying the “basic” design principles of: • Feasibility • Adequacy • Economy • Changeability • Also, The SAD document itself is • Well formed (organized) • Complete (include all the components/relationships/descriptions) • Clear (understandable by others) • Consistent (no conflicting information) (from chapter 8 of text) Think about these for your assignment 3

23. Design Review in Finalizing the SAD • A Review is an examination and evaluation of the work by qualified and affectedstakeholders There are many different types of “reviews”: 1. Desk Check – by the author 2. Walkthrough – informal review by team members 3. Inspection – formal review by a trained inspection team with moderator 4. Audit – review conducted by experts who are not part of the team 5. Active Review – inspection by experts who address specific aspects of the design (this allows pinpoint reviews and is less costly) A “Formal inspection” requires 3 formal steps: - preparation - conducting the inspection - rework and inspection “closeout” report