Architectural Design Resolution Architectural Design Process Analyzed SRS

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

Various Alternatives to Generating Architectural Design 1. Develop Functional Components – from 2. scratch Based on transforming SRS functions and data requirements Determine/Modify Components Based on “Quality Attributes”: maintainability, reusability, performance, availability & security (non-functional attributes) – 3. Based on transforming non-functional SRS requirements Modifying Existing Architecture (for follow-on releases) – 4. Based on existing architecture as a starting point and transforming it to satisfy the new system Elaborate an Architecture Style (chapter 15) – 5. Based on an existing architectural style and elaborate on that style Transform a Conceptual Model (chapter 11 -Destailed Design) – Based on viewing the SRS problem description as a solution description and transforming that to fit the new system

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: 1. Better done as an individual first 2. Bring together all the individual architectural design suggestions 3. Evaluate the alternatives

Determine Functional Components (Using the “Aqua. Lush Irrigation System” Example in textbook – p. 82 and p. 164) Aqua. Lush Product Vision: The Aqua. Lush Irrigation system will use soil moisture sensors to control irrigation, thus saving money for customers and making better use of water resources. Aqua. Lush Major Product Features (from requirements): 1. - Monitor water usage and limit usage (by moisture level) to amounts set by users 2. 3. 4. 5. - 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

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 180 <<component>> Monitor and Repair From page 289 <<component>> User Interface <<component>> Irrigation Control <<component>> Startup Do the functional components and the relation “lines” make sense to you? (Should there be a line between User Interface and Startup ? )

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 <<component>> User Interface <<component>> Monitor and Repair <<component>> Irrigation Control <<read & write>> & ad e Aqua. Lush Parts Status Note that Monitor and Repair component can use the Data Store to communicate with Irrigation Control component, without a line between them. r << w e rit >> <<component>> Startup <<startup reads config. data>> Aqua. Lush Configuration How initiali zed?

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 send them to Irrigation Control & (also 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

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>> e & ad Aqua. Lush Parts Status r << w e rit >> <<component>> Startup <<startup reads config. data>> Aqua. Lush Configuration Same initia lization problem?

Determining Components based on “non-Functional” or “Quality’ attributes • Aqua. Lush has the following non-functional (NF) requirements: – Reusability : design must be used in the product, websimulator, 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

Non. Functional: 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

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

Non. Functional: 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 Virtual Device Interface valve keypad Sensor Agree with all the interaction lines ? Do we need a new component ? display Screen buttons Designer’s view of providing reliability ---- “ not fail often in normal usage”

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 the parts of the generated design alternatives from: • Functional Components • Non-functional Components – Try to alter and fit to an existing Design Style, if applicable

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

Evaluating Architecture Alternatives • What does one look at when evaluating architecture? – Would the architecture result in a system that will satisfy: 1. 2. Functionality requirements “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 can not tell what will happen since the architecture is not code, we can only “guess” whether the architecture will most likely meet the above conditions

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 describes the user requirements (sometimes known as regular “business” workflow) – Reliability profile is a set of scenarios that portrays the nonfunctional requirement of how a system behaves under adverse situations – Performance profile is a set of scenarios that portrays the nonfunctional requirements of how a system behaves under time limit constraints or capacity limit constraints – etc. • Each architecture alternative is evaluated by going through the scenarios in the profile and assessing whether the architecture, if implemented, would satisfy the profile.

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

Another Architecture Evaluating Technique • Build a “prototype” of part of or the complete software product to evaluate certain aspects (functional and non-functional) of the product. – Advantages: • Can provide measurements • Can provide experiential feedbacks – Disadvantages: • Prototypes takes resources • Prototypes takes 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

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

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

Finalizing The Architectural Design • This step ensures that the selected architecture does satisfy 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 (from chapter 8 of text) Think about these for your assignment 4 – Also, The SAD document itself is • • Well formed (organized) Complete (include all the components/relationships/descriptions) Clear (understandable by others) Consistent (no conflicting information)

Design Review in Finalizing the SAD • A Review is an examination and evaluation of the work by qualified and affected stakeholders 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 answer 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