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Dr. Thomas Hicks Computer Science Department Trinity University 1 Software Engineering CSCI 3321
Software Engineering : A Practitioners Approach Agile Development & Real Time Systems Dr. Thomas E. Hicks Computer Science Department Trinity University Thanks To Ian Sommerville & Roger Pressman For Much Of The Slide Content Chapter 4
Agile Development Lite or Lean Methods
We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value: 1. Individuals and interactions over processes and tools 2. Working software over comprehensive documentation 3. Customer collaboration over contract negotiation 4. Responding to change over following a plan That is, while there is value in the items on the right, we value the items on the left more. The Manifesto for Agile Software Development Kent Beck et al The_Agile_Manifesto_SDMagazine.pdf
Agility 1, Everything Else 0 Tom Demarco
Politics Agile Software Development Considerable Debate about the benefits and applicability Pro Agile : Traditional methodologies are a bunch of stick-in-the-muds whod rather produce flawless documentation than a working system that meets business needs. Pro Traditional: Lightweight, agile methodologists are a bunch of glorified hackers who are going to be in for a heck of a surprise when they try to scale up their toys into enterprise-wide software This methodology risks degenerating into a religious war. Pressman
Ivar Jacobson - 1 Agility has become todays buzz word when considering a modern software process. An agile team is a nimble team able to appropriately respond to changes. Changes in the software being built, changes in the team members, changes because of new technology, changes of all kinds that may have impact upon the product they build or the project that creates the product.
Ivar Jacobson – 2 Support for changes should be built-in every thing we do in software, something we embrace because it is the heart and soul of software. An agile team recognizes that software is developed by individuals working in teams and that the skills of those people, their ability to collaborate, is at the core for the success of the project.
7 Human Factors Of Agile Software Development Proponents of the Agile Process emphasize the human factors: 1.Competence – innate talent and overall knowledge of the process – teach needed info to all team members 2.Common Focus – the agile team will focus the different talents working on different portions of the project on the deliverable. 3.Collaboration – quality software requires the collaboration & communication of customer & software engineers 4.Decision Making Ability – teams must be able to make those decisions necessary to control their destiny Pressman
7 Human Factors Of Agile Software Development Proponents of the Agile Process emphasize the human factors: Fuzzy-Problem-Solving-Ability – managers realize teams deal with ambiguity and change – sometimes must accept the fact that problem solving today will be different than problem solving tomorrow – maybe use some of same code. Mutual Trust & Respect – Agile teams must become what DeMarco & Lister call Jelled Teams – whole greater than sum of its parts. Self Organization – self organized to complete work, meet deadlines, etc. Moral booster. Pressman
There is no substitute for rapid feedback, both on the developer process and on the product itself Martin Fowler
12 Principles Adopted By The Agility Conference Highest Priority is to satisfy the customer through early and continuous delivery of valued software. 2. Welcome change requirements even late in the development. Agile processes harness change for the customers competitive advantage. 3. Deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter time scale. 4. Business people, and developers, must work together daily throughout the project.
12 Principles Adopted By The Agility Conference Build projects around motivated individuals. Give them the environment and the support they need. Trust them to get the job done. 6. The most efficient and effective method of conveying information to and within a development team is face to face conversation. 7. Working software is the primary measure of progress. 8. Agile processes promote sustainable development. The sponsors, developers, users should be able to maintain constant pace indefinitely.
12 Principles Adopted By The Agility Conference Continual attention to technical excellence and good design enhances agility. 10. Simplicity, the art of minimizing the amount of work not done, is essential. 11. The best architectures, requirements, and designs emerge from self organizing teams. 12. At regular intervals, the team reflects on how to become more effective, then tunes and tunes and adjusts its behavior accordingly.
Agile Lite Less Time Planning Faster Coding
Agility Software Development Research Tells Us That : Effective response to change; rapid and adaptive Effective communication among all stakeholders Drawing the customer onto the team Organizing a team so that it is in control of the work performed Yields … Rapid, incremental delivery of software
About The Agile Process Agile Process is driven by customer descriptions of what is required; these descriptions are called scenarios Agile Process recognizes that plans are short- lived Agile Process develops software iteratively with a heavy emphasis on construction activities Agile Process delivers multiple software increments Agile Process adapts as changes occur
XP Extreme Programming
Extreme Programming (XP) 4 Step XP Planning Process The most widely used agile process, originally proposed by Kent Beck XP Planning XP Planning 1.XP Planning begins with the creation of user stories 2.An XP Agile team assesses each story and assigns a cost 3.These XP Stories are grouped to for a deliverable increment 4.A commitment is made on delivery date
About Extreme Programming (XP) Design XP Design XP Design follows the KIS principle XP Design encourage the use of CRC cards (see Chapter 8) Class Responsibility Collaborator For difficult design problems, XP suggests the immediate creation of spike solutions; spikes solutions are an operational design prototype of the problem area. XP design encourages refactoring; refactoring an iterative refinement of the internal program design – it is cleaning up the code after it has been written.
XP Coding XP coding recommends the construction of a unit test for a story before coding commences XP coding encourages pair programming – two people work together at one computer to complete code for one story. About Extreme Programming (XP) Coding
XP Testing XP testing recommends that all unit tests be executed daily to encourage regression analysis (i.e. to make sure code still works after it has been modified) XP testing requires acceptance tests, also called customer tests that are defined by the customer and executed to assess customer visible functionality About Extreme Programming (XP) Testing
Extreme Programming is a discipline of software development based on values of simplicity, communication, feedback, and courage. RonJeffries
ASD Adaptive Software Development
Adaptive Software Development (ASD) ASD was originally proposed by Jim Highsmith 6 Distinguishing Features Of ASD ASD uses mission-driven planning; accomplish the task 2.ASD partitions the project into components; it is a component-based focus 3.Uses time-boxing – each task associated with a box; if the project cannot be delivered on time, the work moves forward to the next task when ~90% of the task is complete. Although this is not always acceptable, it is often the case that the last 10% can be completed later.
Adaptive Software Development (ASD) ASD was originally proposed by Jim Highsmith 6 Distinguishing Features Of ASD – ASD explicitly considers all of risks 5.ASD emphasizes collaboration for requirements gathering 6.ASD emphasizes learning throughout the process
3 Major Steps of Adaptive Software Development (ASD) 1. Speculation Use the customer mission statement, project constraints, and basic requirements to define sets of cycles (software releases) for the project. 2. Collaboration The collaboration method is central to all of the agile processes. Using highly motivated people, working collaboratively together to multiply their talents beyond individual expectations. Trust is central. Create Requirements and Mini-Specs. 3. Learning Implement and test components Technical Reviews Focus Group Feedback
Adaptive Software Development
I like to listen. I have learned a great deal from listening carefully. Most people never listen. Ernest Hemingway
DSDM Dynamic Software Development Method
Dynamic Systems Development Method - DSDM DSDM DSDMdistinguishing features Similar in most respects to XP and/or ASD 8 Guiding Principles Of DSDM – Active user involvement is imperative. 2.DSDM teams must be empowered to make decisions. 3.The focus is on frequent delivery of products. 4.Fitness for business purpose is the essential criterion for acceptance of deliverables. Promoted by the DSDM Consortium (www.dsdm.org)www.dsdm.org
Dynamic Systems Development Method - DSDM 8 Guiding Principles Of DSDM Iterative and incremental development is necessary to converge on an accurate business solution. 6.All changes during development are reversible. 7.Requirements are baselined at a high level 8.Testing is integrated throughout the life-cycle.
Dynamic Systems Development Method
Our profession goes through Methodologies like a 14 year-old goes through clothing Stephen Hawrysh & Jim Ruprecht
Scrum – (rugby match term) Developed by Jeff Sutherland in early 1990s Expanded upon by Schwaber and Beedle in 2001 Scrumdistinguishing features – very agile like 1.Scrum has small teams to maximize communication and minimize costs 2.The Scrum process must be adaptable to business and technological changes 3.The Scrum process yields software that can be inspected, adjusted, tested, documented, and built on. 4.The Scrum process partitions the project into low-coupling partitions, or packets.
Scrum (cont) 5.The Scrum process constantly tests and documents as the project is built. 6.The Scrum process provides the ability to declare the product done 7.Scrum work occurs in sprints and is derived from a backlog of existing requirements 8.Scrum meetings are very short and sometimes conducted without chairs 9.Scrum demos are delivered to the customer with the time-box allocated
Scrum allows us to build Software.. Mike Beetle et al.
Crystal Proposed by Cockburn and Highsmith Crystaldistinguishing features Actually a family of process models that allow maneuverability based on problem characteristics Face-to-face communication is emphasized Suggests the use of reflection workshops to review the work habits of the team
FDD Feature Driven Development
Feature Driven Development (FDD) Originally proposed by Peter Coad et al as a process model for OOP FDDdistinguishing features 1. Emphasis is on defining features a feature is a client-valued function that can be implemented in two weeks or less. 2.Uses a feature template the a(n) 3.A features list is created and plan by feature is conducted 4.Design and construction merge in FDD
Feature Driven Development
Agile Modeling Originally proposed by Scott Ambler Suggests a set of agile modeling principles 1.Model with a purpose 2.Use multiple models 3.Travel light 4.Content is more important than representation 5.Know the models and the tools you use to create them 6.Adapt locally
Computer World Computer World Link ware/appdev/story/0,10801,67952,00.html ware/appdev/story/0,10801,67952,00.html
Real Time Software Design
Real-time Software Design Real-time Software Design is designing embedded software systems whose behaviour is subject to timing constraints
Real Time Systems
Real-time systems Real-time systems are used to monitor and control their environment Real-time systems inevitably are associated with hardware devices Sensors: Collect data from the system environment Actuators: Change (in some way) the system's environment Time is critical. Real-time systems MUST respond within specified times
Real-time Definitions A real-time system is a software system where the correct functioning of the system depends on the results produced by the system and the time at which these results are produced A soft real-time system is a system whose operation is degraded if results are not produced according to the specified timing requirements A hard real-time system is a system whose operation is incorrect if results are not produced according to the timing specification
Stimulus & Responses
Stimulus/Response Systems Given a stimulus, the system must produce a response within a specified time Periodic Stimuli: Stimuli which occur at predictable time intervals For example, a temperature sensor may be polled 10 times per second Aperiodic stimuli: Stimuli which occur at unpredictable times For example, a system power failure may trigger an interrupt which must be processed by the system
Architectural Considerations Because of the need to respond to timing demands made by different stimuli/responses, the system architecture must allow for fast switching between stimulus handlers Timing demands of different stimuli are different so a simple sequential loop is not usually adequate Real-time systems are usually designed as cooperating processes with a real-time executive controlling these processes
A Real-time System Model
Real Time System Elements
Real-time System Elements Sensors control processes Collect information from sensors. May buffer information collected in response to a sensor stimulus Data processor Carries out processing of collected information and computes the system response Actuator control Generates control signals for the actuator
Real Time Design Hardware & Software
Real-time System Design – 2 Stages Real-time system engineers must design both the hardware and the software associated with system. Real-time system engineers then partition functions to either hardware or software Design decisions should be made on the basis on non-functional system requirements Hardware delivers better performance but potentially longer development and less scope for change
Hardware & Software Design
R-T Systems Design Process – 6 Steps 1. The first step in the R-T design process is to identify the stimuli to be processed and the required responses to these stimuli 2. The second step in the R-T design process is to identify the timing constraints for each stimulus and response 3. The third step in the R-T design process is to aggregate the stimulus and response processing into concurrent processes. A process may be associated with each class of stimulus and response.
The fourth step in the R-T design process is to design algorithms for each concurrent process. These must meet the given timing requirements The fifth step in the R-T design process is to design a scheduling system which will ensure that processes are started in time to meet their deadlines The sixth step in the R-T design process is to integrate the real-time executive with an operating system (if necessary) R-T Systems Design Process – 6 Steps
Real Time Timing Constraints
Timing Constraints Meeting timing constraints may require extensive simulation and experiment to ensure that these are met by the system Meeting timing constraints may mean that certain design strategies such as object-oriented design cannot be used because of the additional overhead involved Meeting timing constraints may mean that low- level programming language features have to be used for performance reasons
Real Time State Machines
State Machine Modelling The effect of a stimulus in a real-time system may trigger a transition from one state to another. Finite state machines can be used for modelling real-time systems. However, FSM models lack structure. Even simple systems can have a complex model. The UML includes notations for defining state machine models
Microwave Oven State Machine
Real Time Programming
Real-time Programming & Languages Hard-real time systems may have to programmed in assembly language to ensure that deadlines are met Languages such as C allow efficient programs to be written but do not have constructs to support concurrency or shared resource management Ada as a language designed to support real-time systems design so includes a general purpose concurrency mechanism
Java As a Real-time Language Java supports lightweight concurrency (threads and synchronized methods) and can be used for some soft real-time systems Java 2.0 is not suitable for hard RT programming or programming where precise control of timing is required 1.Not possible to specify thread execution time 2.Uncontrollable garbage collection 3.Not possible to discover queue sizes for shared resources 4.Variable virtual machine implementation 5.Not possible to do space or timing analysis
Real Time Executives
Real-time Executives Real-time executives are specialized operating systems which manage the processes in the RTS Real-time executives are responsible for process management and resource (processor and memory) allocation Real-time executives may be based on a standard RTE kernel which is used unchanged or modified for a particular application Real-time executives do not include facilities such as file management 14
R-T Executive Components Real-time clock Provides information for process scheduling. Interrupt handler Manages aperiodic requests for service. Scheduler Chooses the next process to be run. Resource manager Allocates memory and processor resources. Dispatcher Starts process execution.
R-T Non-stop System Components Configuration manager Responsible for the dynamic reconfiguration of the system software and hardware. Hardware modules may be replaced and software upgraded without stopping the systems Fault manager Responsible for detecting software and hardware faults and taking appropriate actions (e.g. switching to backup disks) to ensure that the system continues in operation
Real-time Executive Components
Real Time Process Priority & Servicing
R-T Process Priority The processing of some types of stimuli must sometimes take priority Interrupt level priority. Highest priority which is allocated to processes requiring a very fast response Clock level priority. Allocated to periodic processes Within these, further levels of priority may be assigned
R-T Interrupt Servicing Control is transferred automatically to a pre-determined memory location This location contains an instruction to jump to an interrupt service routine Further interrupts are disabled, the interrupt serviced and control returned to the interrupted process Interrupt service routines MUST be short, simple and fast
R-T Periodic Process Servicing In most real-time systems, there will be several classes of periodic process, each with different periods (the time between executions), execution times and deadlines (the time by which processing must be completed) The real-time clock ticks periodically and each tick causes an interrupt which schedules the process manager for periodic processes The process manager selects a process which is ready for execution
Real Time Process Management
R-T Process Management Concerned with managing the set of concurrent processes Periodic processes are executed at pre-specified time intervals The executive uses the real-time clock to determine when to execute a process Process period - time between executions Process deadline - the time by which processing must be complete
R-T Process Management
Process Switching The scheduler chooses the next process to be executed by the processor. This depends on a scheduling strategy which may take the process priority into account The resource manager allocates memory and a processor for the process to be executed The dispatcher takes the process from ready list, loads it onto a processor and starts execution
Real Time Scheduling Strategies
R-T Scheduling Strategies Non pre-emptive scheduling Once a process has been scheduled for execution, it runs to completion or until it is blocked for some reason (e.g. waiting for I/O) Pre-emptive scheduling The execution of an executing processes may be stopped if a higher priority process requires service Scheduling algorithms Round-robin Rate monotonic Shortest deadline first
Real Time Monitoring & Control Systems
Monitoring & Control Systems Monitoring & control systems are an important class of real-time systems Monitoring & control systems continuously check sensors and take actions depending on sensor values Monitoring systems examine sensors and report their results Control systems take sensor values and control hardware actuators
Real Time Monitoring Systems Burglar Alarm
Designing A Burglar Alarm System Example Of A Monitoring System A system is required to monitor sensors on doors and windows to detect the presence of intruders in a building When a sensor indicates a break-in, the system switches on lights around the area and calls police automatically The system should include provision for operation without a mains power supply
Sensors Movement detectors, window sensors, door sensors. 50 window sensors, 30 door sensors and 200 movement detectors Voltage drop sensor Actions When an intruder is detected, police are called automatically. Lights are switched on in rooms with active sensors. An audible alarm is switched on. The system switches automatically to backup power when a voltage drop is detected. Sensors & Actions Of A Burglar Alarm System Example Of A Monitoring System
Real Time System Design
The 5 Step R-T System Design Process 1. Identify stimuli and associated responses 2. Define the timing constraints associated with each stimulus and response 3. Allocate system functions to concurrent processes 4. Design algorithms for stimulus processing and response generation 5. Design a scheduling system which ensures that processes will always be scheduled to meet their deadlines
Stimuli To Be Processed - A Burglar Alarm System Power failure Generated aperiodically by a circuit monitor. When received, the system must switch to backup power within 50 ms Intruder alarm Stimulus generated by system sensors. Response is to call the police, switch on building lights and the audible alarm
A Burglar Alarm Systems Timing Requirements
A Burglar Alarm Systems Architecture Diagram
Building_monitor process 1 A Burglar Alarm Systems Sample Code
Building_monitor process 2 A Burglar Alarm Systems Sample Code
Real Time Control Systems Temperature Control
Control Systems A burglar alarm system is primarily a monitoring system. It collects data from sensors but no real-time actuator control Control systems are similar but, in response to sensor values, the system sends control signals to actuators An example of a monitoring and control system is a system which monitors temperature and switches heaters on and off
A Temperature Control System
Data Acquisition Systems Data Acquisition Systems collect data from sensors for subsequent processing and analysis. Data collection processes and processing processes may have different periods and deadlines. Data collection may be faster than processing e.g. collecting information about an explosion. Circular or ring buffers are a mechanism for smoothing speed differences.
Nuclear Reactor Data Collection Another Control System Example A system collects data from a set of sensors monitoring the neutron flux from a nuclear reactor. Flux data is placed in a ring buffer for later processing. The ring buffer is itself implemented as a concurrent process so that the collection and processing processes may be synchronized.
Nuclear Reactor Flux Monitoring Another Control System Example
A Ring Buffer
Mutual Exclusion Producer processes collect data and add it to the buffer. Consumer processes take data from the buffer and make elements available Producer and consumer processes must be mutually excluded from accessing the same element. The buffer must stop producer processes adding information to a full buffer and consumer processes trying to take information from an empty buffer.
Java implementation of a ring buffer 1 A Circular Buffer Sample Code
Java implementation of a ring buffer 2 A Circular Buffer Sample Code
Software Engineering CSCI 3342 Dr. Thomas E. Hicks Computer Science Department Trinity University Textbook: Software Engineering By Roger Pressman Textbook: Software Engineering By Ian Sommerville Special Thanks To WCB/McGraw-Hill & Addison Wesley For Providing Graphics Of Some Of Text Book Figures For Use In This Presentation.