Software and Software Engineering

Software and Software Engineering.

The nature of software. Software is intangible Hard to understand development effort Software is easy to reproduce Cost is in its development in other engineering products, manufacturing is the costly stage The industry is labor-intensive Hard to automate.

The nature of software. Untrained people can hack something together Quality problems are hard to notice Software is easy to modify People make changes without fully understanding it Software does not ‘wear out’ It deteriorates by having its design changed: erroneously, or in ways that were not anticipated, thus making it complex.

Software crisis???. Much software has poor design and is getting worse Many software projects are either never delivered, or are delivered late and over budget There is strong demand for new and changed software, which customers expect to be of high quality and to be produced rapidly. Are we in a perpetual ‘software crisis’???.

Types of software.... Custom For a specific customer Generic Sold on open market Often called COTS (Commercial Off The Shelf) Shrink-wrapped Embedded Built into hardware Hard to change.

Types of software. Differences among custom, generic and embedded software.

Types of software. Real time software E.g. control and monitoring systems Must react immediately Safety often a concern Data processing software Used to run businesses Accuracy and security of data are key Some software has both aspects.

What is software engineering?. The process of solving customers’ problems by the systematic development and evolution of large, high-quality software systems within cost, time and other constraints Other definitions: IEEE: (1) the application of a systematic, disciplined, quantifiable approach to the development, operation, maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1). The Canadian Standards Association: The systematic activities involved in the design, implementation and testing of software to optimize its production and support..

What is software engineering?. Solving customers’ problems This is the goal of software engineering Sometimes the solution is to buy, not build Adding unnecessary features does not help solve the problem Software engineers must communicate effectively to identify and understand the problem.

What is software engineering?. Systematic development and evolution An engineering process involves applying well understood techniques in an organized and disciplined way Many well-accepted practices have been formally standardized e.g. by the IEEE or ISO Most development work is evolution.

What is software engineering?. Large, high quality software systems Software engineering techniques are needed because large systems cannot be completely understood by one person Teamwork and co-ordination are required Key challenge: Dividing up the work and ensuring that the parts of the system work properly together The end-product must be of sufficient quality.

What is software engineering?. Cost, time and other constraints Finite resources The benefit must outweigh the cost Others are competing to do the job cheaper and faster Inaccurate estimates of cost and time have caused many project failures.

Software engineering and the engineering profession.

Ethics in software engineering. Software engineers shall Act consistently with public interest Act in the best interests of their clients Develop and maintain with the highest standards possible Maintain integrity and independence Promote an ethical approach in management Advance the integrity and reputation of the profession Be fair and supportive to colleagues Participate in lifelong learning.

Stakeholders in software engineering. 1. Users Those who use the software 2. Customers Those who pay for the software 3. Software developers Requirement specialists Database specialists Programmers Configuration management specialists 4. Development Managers All four roles can be fulfilled by the same person.

Software quality. Usability Users can learn it and fast and get their job done easily Efficiency It doesn't’t waste resources such as CPU time and memory Reliability It does what it is required to do without failing Maintainability It can be easily changed Reusability Its parts can be used in other projects, so reprogramming is not needed.

Software quality and the stakeholders. QUALITY SOFTWARE.

Software quality: conflicts and objectives. The different qualities can conflict Increasing efficiency can reduce maintainability or reusability Increasing reliability can reduce efficiency Setting objectives for quality is a key engineering activity You then design to meet the objectives Avoids ‘over-engineering’ which wastes money Optimizing is also sometimes necessary E.g. obtain the highest possible reliability using a fixed budget.

Internal quality criteria. These: Characterize aspects of the design of the software Have an effect on the external quality attributes E.g. The amount of commenting of the code The complexity of the code.

Short term vs. long term quality. Short term: Does the software meet the customer’s immediate needs? Is it sufficiently efficient for the volume of data we have today? Long term: Maintainability Customer’s future needs Scalability: Can the software handle larger volumes of data?.

Software engineering projects. Most projects are evolutionary or maintenance projects, involving work on legacy systems Corrective projects: fixing defects Adaptive projects: changing the system in response to changes in Operating system Database Rules and regulations Enhancement projects: adding new features for users Reengineering or perfective projects: changing the system internally so it is more maintainable.

Software engineering projects. ‘Green field’ projects New development Significantly less common than evolutionary projects.

Software engineering projects. Projects that involve building on a framework or a set of existing components. A framework is an application that is missing some important details E.g. Specific rules of this organization Such projects: Involve plugging together components that are: Already developed Provide significant functionality Benefit from reusing reliable software Provide much of the same freedom to innovate found in green field development.

Activities common to software projects. Requirements and specification Includes Domain analysis Defining the problem Requirements gathering Obtaining input from as many sources as possible Requirements analysis Organizing the information Requirements specification (Specs, SRS , Req. Doc.) Writing detailed instructions about how the software should behave.

Activities common to software projects. Design Deciding how the requirements should be implemented, using the available technology Includes: Systems engineering: Deciding what should be in hardware and what in software Software architecture: Dividing the system into subsystems and deciding how the subsystems will interact Detailed design of the internals of a subsystem User interface design Design of databases.

Activities common to software projects. Modeling Creating representations of the domain or the software Use case modeling Structural modeling Dynamic and behavioral modeling Programming Quality assurance Reviews and inspections Testing Deployment Managing the process.

Difficulties and risks in software engineering. Complexity and large numbers of details Uncertainty about technology Uncertainty about requirements Uncertainty about software engineering skills Constant change Deterioration of software design Political risks.

Lady Augusta Ada Lovelace (1815-1852) was the world's first programmer! If debugging is the process of removing bugs, then programming must be the process of putting them in... This beautiful picture of Lady Ada was painted by Latvian artist Inta Dobraja in 1986 and currently decorates the Department of Computer Science at Latvia University, Riga, Latvia..

The first bug  September 9, 1947. 1S4s- case. 29.

An F-16 (northern hemisphere). [image]. 30.

The same F-16 (southern hemisphere). [image]. 31.

F-16 landing gear. 32.

Famous Software Disasters. Mars Climate Crasher (1998) Cost: $125 million Disaster: After a 286-day journey from Earth, the Mars Climate Orbiter fired its engines to push into orbit around Mars. The engines fired, but the spacecraft fell too far into the planet’s atmosphere, likely causing it to crash on Mars. Cause: The software that controlled the Orbiter thrusters used imperial units (pounds of force), rather than metric units (Newton) as specified by NASA. http://www.devtopics.com/20-famous-software-disasters-part-1/.

Famous Software Disasters. AT&T Lines Go Dead (1990) Cost: 75 million phone calls missed, 200 thousand airline reservations lost Disaster: A single switch at one of AT&T’s 114 switching centers suffered a minor mechanical problem and shut down the center. When the center came back up, it sent a message to other switching centers, which in turn caused them to shut down and brought down the entire AT&T network for 9 hours. Cause: A single line of buggy code in a complex software upgrade implemented to speed up calling caused a ripple effect that shut down the network. (more).

Famous Software Disasters. World War III… Almost (1983) Cost: Nearly all of humanity Disaster: The Soviet early warning system falsely indicated the United States had launched five ballistic missiles. Fortunately the Soviet duty officer had a “funny feeling in my gut” and reasoned if the U.S. was really attacking they would launch more than five missiles, so he reported the apparent attack as a false alarm. Cause: A bug in the Soviet software failed to filter out false missile detections caused by sunlight reflecting off cloud-tops. (more).