CEN 5011 Advanced Software Engineering Software Life Cycle Instructor: Masoud Sadjadi http://www.cs.fiu.edu/~sadjadi/Teaching/

Acknowledgements Dr. Peter Clarke Dr. Betty Cheng Dr. Bernd Bruegge Dr. Allen Dutoit

Agenda Overview Terminology Software Processes Software Life Cycle Good Software!

Our Intention Requirements Software

Our plan of attack Requirements Analysis Design Implementation Testing Delivery and Installation

How it often goes Requirements D E L A Y Analysis Vaporware

Courtesy of an anonymous artist. Found on the Web! Today’s Practice! Courtesy of an anonymous artist. Found on the Web!

Inherent Problems Requirements are complex The client does not know the functional requirements in advance. Requirements may be changing Technology enablers introduce new possibilities to deal with nonfunctional requirements. Frequent changes are difficult to manage Identifying milestones and cost estimation is difficult. There is more than one software system Backward compatible with existing systems Let’s view these problems as the nonfunctional requirements for a system that supports software development! This leads us to software life cycle modeling

Agenda Overview Terminology Software Processes Software Life Cycle Good Software!

Terminology (1) participants – all persons involved in a project. e.g., developers, project manager, client, end users. role – associated with a set of tasks assigned to a participant. system – underlying reality. model – abstraction of the reality. work product – an artifact produced during development.

Terminology (2) deliverable – work product for client. activity – a set of tasks performed toward a specific purpose. milestone – end-point of a software process activity. task – an atomic unit of work that can be managed and that consumes resources. goal – high-level principle used to guide the project.

Terminology (3) functional requirement – describes the interaction between the system and its actors (e.g., end users and other external systems) independent of its implementation. nonfunctional requirement – describes aspects of the system that are not directly related to the functional requirements of the system (e.g., QoS, security, scalability, performance, and fault-tolerance). notation – is a graphical or textual set of rules representing a model (e.g., UML) method – a repeatable technique for solving a specific problem e.g. sorting algorithm methodology – a collection of methods for solving a class of problems (e.g., Unified Software Development Process).

Agenda Overview Terminology Software Processes Software Life Cycle Good Software!

Software Processes Specification Development Validation Evolution requirements elicitation and analysis. Development systems design, detailed design (OO design), implementation. Validation validating system against requirements (testing). Evolution meet changing customer needs and error correction (maintenance).

Software Specification (1) Functionality of the software and constraints (non-functional requirements) on its operation must be defined. Involves: Requirements elicitation The client and developers define the purpose of the system. Output is a description of the system in terms of actors and uses cases. Actors include roles such as end users and other computers the system needs.

Software Specification (2) Uses cases are general sequences of events that describe all possible actions between actor and the system for a given piece of functionality. Analysis Objective: produce a model of the system that is correct, complete, consistent, unambiguous, realistic, and verifiable. Developers transform the use cases into an object model that completely describes the system. Model is checked for ambiguities and inconsistencies. Output: Object model annotated with attributes, operations, and associations.

Software Development (1) Producing the software that meets the specification. System Design Goals of the project are defined. System decomposed into smaller subsystems (architectural model). Strategies to build system identified HW and SW platform, data management, control flow, and security. Output: model describing subsystem decomposition and system strategies.

Software Development (2) Object Design Bridges the gap between analysis model and the strategies identified in the system design. Includes: Describing object and subsystem interfaces Selecting off–the-shelf components Restructure object model to attain design goals e.g., extensibility, understandability, and required performance. Output: detailed object model annotated with constraints and supporting documentation. Implementation Translation of the object model into source code. No general process followed. There are tools to assists the programmer such as CASE tools.

Software Development Activities Requirements Analysis What is the problem? System Design What is the solution? Problem Domain Implementation Domain Object Design What is the solution in a specific context? Implementation How is the solution constructed?

Software Validation (1) Ensures the software does what the customer want. The software conforms to its specification and meets the expectations of the customer. Validation: ‘Are we building the right product?’ Ensures the software meets the expectations of the customer. Verification: ‘Are we building the product right?’ Ensures the software conforms to the specification.

Software Validation (2) Techniques Software inspections (static): Analyze and check system representations (e.g., requirements documents, design diagrams, and program source code). Software testing (dynamic): Executing an implementation of the software with test data and examining the outputs against expected results. V&V process establishes the existence of defects. Debugging is a process that locates and corrects these defects.

Software Evolution Software must evolve to meet the customer needs. Software maintenance is the process of changing a system after it has been delivered. Reasons for maintenance To repair faults. To adapt the software to a different operating environment. To add to or modify system’s functionality.

Agenda Overview Terminology Software Processes Software Life Cycle Good Software!

Software Life Cycle Software life cycle modeling Software life cycle Attempt to deal with complexity and change. Software life cycle Set of activities and their relationships to each other to support the development of a software system . Software development methodology A collection of techniques for building models, which are applied across the software lifecycle.

Software Life Cycle Software construction goes through a progression of states Adulthood Childhood Retirement Conception Pre- Development Post- Development Development

Software Life Cycle Models Waterfall model and its problems Pure Waterfall Model V-Model Iterative process models Boehm’s Spiral Model Unified Process Model Entity-based models Issue-based Development Model Concurrent Development

Waterfall Model (1) The waterfall model First described by Royce in 1970 There seem to be at least as many versions as there are authorities - perhaps more Requirements Definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance

Waterfall Model (2) One or more documents are produced after each phase and “signed off”. Points to note: “Water does not flow up”. it is difficult to change artifact produced in the previous phase. This model should be used only when the requirements are well understood. Reflects engineering practice. Simple management model.

From Waterfall to V Model Horizontal lines denote the information flow between activities at the same abstraction level. Requirements Specification System design Detailed Design Implementation Unit Test System and integration test Acceptance test

V Model Similar to pure waterfall model but makes explicit the dependency between development and verification activities. The left half of the V represents development and the right half system validation. Note the requirements specification includes systems reqs. analysis, reqs. elicitation, and reqs. analysis.

Spiral Model (1) Basic Idea Two types: Advantages Disadvantages develop initial implementation, expose it to user, and refine it until an adequate system is produced. Two types: Exploratory Throw-away prototyping Advantages model used when problem is not clearly defined. Disadvantages Process not visible, systems are poorly constructed, may require special tools and techniques.

Spiral Model (2) Design objectives, Evaluate alternatives, alternatives, and constraints Evaluate alternatives, identify and resolve risks Risk analysis Risk analysis Risk analysis Prototype 3 Not shown in detail Prototype 2 Prototype 1 Requirements plan Concept of operation S/w Reqs. Detailed Design Sys. Product Design Development Plan Reqs. Validation Code Integration Plan Design Validation Unit Test Integration & Test Acceptance Test Develop and verify next level product Plan next phase

Spiral Model (3) Tries to accommodate infrequent change during development. Each round of the spiral involves: Determine objectives Specify constraints Generate alternatives Identify risks Resolve risks Develop and verify next level product Plan

Incremental Development (1) Mills et al. 1980 Define outline requirements Assign requirements to increments Design system architecture Develop system increment Validate Integrate system System incomplete Final

Incremental Development (2) Software specification, design and implementation is broken down into a series of increments which are developed in turn. Gives customers some opportunities to delay decisions on the detailed requirements of the system. Services are identified and a priority allocated. Each increment provides a subset of the system’s functionality.

Incremental Development (3) Advantages: Customers do not have to wait for the entire system. Customers gain experience using early increments of the system. Lowers the risk of overall project failure. Most important system services receives the most testing. Disadvantages: May be difficult to map meaningful functionality into small increments.

Extreme Programming The incremental approach has evolved to ‘extreme programming’ (Beck 1988). Extreme programming: Development and delivery of very small increments. Customer involvement in the process. Constant code improvement. Egoless programming Programs are regarded as group property!

Unified Software Development Process (1) Similar to Boehm’s spiral model. A project consists of several cycles, each ends with the delivery of a product to the customer. Each cycle consists of four phases: Inception Elaboration Construction Transition Each phase consists of a number of iterations.

Unified Software Development Process (2) Inception ends with commitment from the project sponsor to go ahead. Elaboration ends with basic architecture of the system in place, a plan for construction agreed, all significant risks identified, and major risks understood enough not to be too worried. Construction ends with a beta-release system. Transition is the process of introducing the system to it users.

Unified Software Development Process (2) System Development Analysis model specified by realized by Design model Use case model distributed by Deployment model implemented by Implementation model Requirements captured as a set of use cases. verified by Test model

Unified Software Development Process (3) Deployment model physical communication links between hardware items. relationships between physical machines and processes. The models in the Unified Process are traceable A model element can be traced to at least one element in an associated model. Transition between models are seamless we can tell in a foreseeable way how to get from an element in one model to one/more elements in an associated model.

Issue-Based Development A system is described as a collection of issues Issues are either closed or open. Closed issues have a resolution. Closed issues can be reopened (Iteration!). The set of closed issues is the basis of the system model I1:Open I2:Closed I3:Closed A.I1:Open A.I2:Open SD.I1:Closed SD.I2:Closed SD.I3:Closed Planning Requirements Analysis System Design

What to Choose? PT = Project Time, MTBC = Mean Time Between Change Change rarely occurs (MTBC >> PT): Waterfall Model All issues in one phase are closed before proceeding to the next phase Change occurs sometimes (MTBC = PT): Boehm’s Spiral Model Change occurring during a phase might lead to an iteration of a previous phase or cancellation of the project “Change is constant” (MTBC << PT) Issue-based Development (Concurrent Development Model) Phases are never finished, they all run in parallel Decision when to close an issue is up to management. The set of closed issues form the basis for the system to be developed.

Agenda Overview Terminology Software Processes Software Life Cycle Good Software!

Attributes of Good Software Maintainability Ease of changing the software to meets the changing needs of the customer. Dependability Reliability, security and safety. Efficiency Responsiveness, processing time, and memory usage. Usability Appropriate user interface and adequate documentation.

Capability Maturity Model (CMM) 1. Initial Level ad hoc, no feedback from user, black box. 2. Repeatable Level Each project has a well-defined sw life cycle model. 3. Defined Level A document sw life cycle model for all managerial and technical activities across the org. exists. 4. Managed Level Metrics for activities and deliverables are defined. 5. Optimizing Level Process allows feedback of information to change process itself. Note: In 2000, the SW-CMM was upgraded to CMMI® (Capability Maturity Model Integration).

State of the Software Industry in 1995 Maturity Level Frequency 1. Initial 70% 2. Repeatable 15% 3. Defined < 10% 4. Managed < 5% 5. Optimizing < 1% Source: Royce, Project Management, P. 364