CSCI 310 Midterm 1

abstraction

"The act or process of separating in thought, of considering a thing independently of its associations; or a substance independently of its attributes; or an attribute or quality independently of the substance to which it belongs."

reification

"The mental conversion of ... [an] abstract concept into a thing."

deduction

"The process of drawing a conclusion from a principle already known or assumed; spec. in Logic, inference by reasoning from generals to particulars; opposed to INDUCTION."

induction

"The process of inferring a general law or principle from the observation of particular instances (opposed to DEDUCTION, q.v.)."

client-server style

-Components are clients and servers -Servers do not know number or identities of clients -Clients know server's identity -Connectors are RPC-based network interaction protocols

"principal"

-Implies a degree of importance that grants a design decision "architectural status" -Implies that not all design decisions are architectural --They do not necessarily impact a system's architecture -How one defines "principal" will depend on what the stakeholders define as the system goals

methods

Structured approaches to software development which include system Models - why? Notations - Such as? Rules - constraints applied to system models Design advice - recommendations on good design practice Process guidance - what activities to follow What are some example methods?

software engineering vs systems engineering

Systems engineering - concerned with all aspects of computer-based systems development including hardware, software, and process engineering. Software engineering - a "component" in this process Systems engineers are involved in overall system specification, architectural design, integration and deployment

software component

Elements that encapsulate processing and data in a system's architecture -A software component is an architectural entity that --encapsulates a subset of the system's functionality and/or data --restricts access to that subset via an explicitly defined interface --has explicitly defined dependencies on its required execution context -Typically provide application-specific services

essential attributes of good software (4)

Maintainability: Software should be written in such a way so that it can evolve to meet the changing needs of customers. This is a critical attribute because software change is an inevitable requirement of a changing business environment. Dependability/security: Software dependability includes a range of characteristics including reliability, security and safety. Dependable software should not cause physical or economic damage in the event of system failure. Malicious users should not be able to access or damage the system. Efficiency: Software should not make wasteful use of system resources such as memory and processor cycles. Efficiency therefore includes responsiveness, processing time, memory utilisation, etc. Acceptability: Software must be acceptable to the type of users for which it is designed. This means that it must be understandable, usable and compatible with other systems that they use.

examples of software connectors

Procedure call connectors Shared memory connectors Message passing connectors Streaming connectors Distribution connectors Wrapper/adaptor connectors

Mythical Man Month by Fred Brooks

Published in 1975, republished in 1995 Experience managing development of OS/360 in 1964-65 Central argument: Large projects suffer management problems different in kind than small ones due to division of labor, critical need is the preservation of the conceptual integrity of the product itself Central conclusions: Conceptual integrity achieved through chief architect, implementation achieved through well-managed effort Brooks's Law: Adding personnel to a late project makes it later

parallels between the architecture of buildings and software

Obvious: -Satisfaction of customers' needs -Specialization of labor -Multiple perspectives of the final product -Intermediate points where plans and progress are reviewed Deeper: -Architecture is different from, but linked with, the product/structure -Properties of structures are induced by the design of the architecture -The architect has a distinctive role and character -Architecture has matured over time into a discipline --Wide range of solutions, techniques, and palettes of different "materials", "colors", and "sizes"

software costs

Often dominate computer system costs (software on a PC > hardware cost) Software costs more to maintain than it does to develop. For systems with a long life, maintenance costs may be several times development costs. Software engineering is concerned with cost-effective software development 60% development costs, 40% are testing costs Evolution/maintenance costs > development costs Costs vary depending on: -The type of system being developed (custom built vs. mass market software) -The requirements of system attributes such as performance and system reliability -The experience of the development team(s) Distribution of costs depends on the development model that is used

The waterfall model

Plan-driven model. Separate and distinct phases of specification and development. Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance Drawback - the difficulty of accommodating change after the process is underway; a phase has to be complete before moving onto the next phase

architectural recovery

Process of determining a software system's architecture from its implementation-level artifacts, which can include: -Source code -Executable files -Java .class files

why are there difficulties?

a unique brand of engineering: Software is malleable Software construction is human-intensive Software is intangible Software problems are unprecedentedly complex Software directly depends on the hardware It is at the top of the system engineering "food chain" Software solutions require unusual rigor Software has discontinuous operational nature

WWW in a nutshell

-A collection of resources, each of which has a unique name known as a uniform resource locator, or "URL". -Each resource denotes, informally, some information. -URI's can be used to determine the identity of a machine on the Internet, known as an origin server, where the value of the resource may be ascertained. -Communication is initiated by clients, known as user agents, who make requests of servers. -Web browsers are common instances of user agents. -Resources can be manipulated through their representations. -HTML is a very common representation language used on the Web. -All communication between user agents and origin servers must be performed by a simple, generic protocol (HTTP), which offers the command methods GET, POST, etc. -All communication between user agents and origin servers must be fully self-contained. (So-called "stateless interactions")

deployment

-A software system cannot fulfill its purpose until it is deployed -Executable modules are physically placed on the hardware devices on which they are supposed to run -The deployment view of an architecture can be critical in assessing whether the system will be able to satisfy its requirements: --Possible assessment dimensions --Available memory --Power consumption --Required network bandwidth

extreme programming

-A very influential agile method, developed in the late 1990s, that introduced a range of agile development techniques. -Takes an 'extreme' approach to iterative development. --New versions may be built several times per day; --Increments are delivered to customers every 2 weeks; --All tests must be run for every build and the build is only accepted if tests run successfully.

process improvement

-A way of enhancing the quality of their software, reducing costs or accelerating their development processes. -Means understanding existing processes and changing these processes to increase product quality and/or reduce costs and development time. Measure -> Analyze -> Change (repeat)

architecture of WWW

-Architecture of the Web is wholly separate from the code -There is no single piece of code that implements the architecture. -There are multiple pieces of code that implement the various components of the architecture. --E.g., different Web browsers

reducing reworking costs (2)

-Change anticipation - software process includes activities that can anticipate possible changes before significant rework is required (a prototype system may be developed to show some key features of the system to customers) -Change tolerance - process is designed so that changes can be accommodated at relatively low cost (normally involves some form of incremental development) --Proposed changes may be implemented in increments that have not yet been developed.

coping with change

-Change is inevitable in all large software projects. -Business changes lead to new and changed system requirements -New technologies open up new possibilities for improving implementations -Changing platforms require application changes -Change leads to rework so the costs of change include both rework (e.g. re-analyzing requirements) as well as the costs of implementing new functionality

essential difficulties (4)

-Complexity: no two software parts are alike complexity grows non-linearly with size -Conformity: software is always required to conform often the "last kid on the block" -Changeability: software is viewed as infinitely malleable change originates with new applications, users, machines, standards, laws -Invisibility: the reality of software is not embedded in space software is not representable as a familiar geometric entity

pipe and filter style

-Components are filters --Transform input data streams into output data streams --Possibly incremental production of output -Connectors are pipes --Conduits for data streams -Style invariants --Filters are independent (no shared state) --Filter has no knowledge of up- or down-stream filters -Examples: UNIX shell signal processing Distributed systems parallel programming -Example: ls invoices | grep -e August | sort Advantages: -System behavior is a succession of component behaviors -Filter addition, replacement, and reuse --Possible to hook any two filters together -Certain analyses --Throughput, latency, deadlock -Concurrent execution Disadvantages: -Batch organization of processing -Interactive applications -Lowest common denominator on data transmission

object-oriented style

-Components are objects --Data and associated operations -Connectors are messages and method invocations -Style invariants --Objects are responsible for their internal representation integrity --Internal representation is hidden from other objects Advantages: -"Infinite malleability" of object internals -System decomposition into sets of interacting agents Disadvantages: -Objects must know identities of servers -Side effects in object method invocations

objectives of architectural design

-Creativity --Enhance your skill-set --Provide new tools -Method --Focus on highly effective techniques -Develop judgment --When to develop novel solutions, and when to follow established method

principles of agile (5)

-Customer involvement --Customers should be closely involved throughout the development process. Their role is to provide and prioritize new system requirements and to evaluate the iterations of the system. -Incremental delivery --The software is developed in increments with the customer specifying the requirements to be included in each increment. -People not process --The skills of the development team should be recognized and exploited. Team members should be left to develop their own ways of working without prescriptive processes. -Embrace change --Expect the system requirements to change and so design the system to accommodate these changes. -Maintain simplicity --Focus on simplicity in both the software being developed and in the development process. Wherever possible, actively work to eliminate complexity from the system.

advantages of incremental delivery

-Customer value can be delivered with each increment so system functionality is available earlier. -Early increments act as a prototype to help elicit requirements for later increments. -Lower risk of overall project failure. -The highest priority system services tend to receive the most testing.

temporal aspect of software architecture

-Design decisions are and unmade over a system's lifetime -At any given point in time, the system has only one architecture -A system's architecture will change over time

implicit invocation style

-Event announcement instead of method invocation --"Listeners" register interest in and associate methods with events --System invokes all registered methods implicitly -Component interfaces are methods and events -Two types of connectors --Invocation is either explicit or implicit in response to events -Style invariants --"Announcers" are unaware of their events' effects --No assumption about processing in response to events Advantages: -Component reuse -System evolution --Both at system construction-time & run-time Disadvantages: -Counter-intuitive system structure -Components relinquish computation control to the system -No knowledge of what components will respond to event -No knowledge of order of responses

influence of XP

-Extreme programming has a technical focus and is not easy to integrate with management practice in most organizations. -While agile development uses practices from XP, the method as originally defined is not widely used. Key practices: -User stories for specification -Refactoring -Test-first development -Pair programming

general issues that affect software (4)

-Heterogeneity: Increasingly, systems are required to operate as distributed systems across networks that include different types of computer and mobile devices. -Business and social change: Business and society are changing incredibly quickly as emerging economies develop and new technologies become available. They need to be able to change their existing software and to rapidly develop new software. -Security and trust: As software is intertwined with all aspects of our lives, it is essential that we can trust that software. -Scale: Software has to be developed across a very wide range of scales, from very small embedded systems in portable or wearable devices through to Internet-scale, cloud-based systems that serve a global community.

layered style

-Hierarchical system organization -Each layer exposes an interface (API) to be used by above layers -Each layer acts as a: --Server: service provider to layers "above" --Client: service consumer of layer(s) "below" -Connectors are protocols of layer interaction -Example: operating systems -Virtual machine style results from fully opaque layers Advantages: -Increasing abstraction levels -Evolvability -Changes in a layer affect at most two layers -Different implementations are allowed as long as interface is preserved -Standardized layer interfaces for libraries/frameworks Disadvantages: -Not universally applicable -Performance -Layers may have to be skipped -Determining the correct abstraction level

XP and agile principles

-Incremental development is supported through small, frequent system releases. -Customer involvement means full-time customer engagement with the team. -People not process through pair programming, collective ownership and a process that avoids long working hours. -Change supported through regular system releases. -Maintaining simplicity through constant refactoring of code.

building product lines

-Reusing structure, behaviors, and component implementations is increasingly important to successful business practice --Simplifies the software development task --Reduces the development time and cost --Improves the overall system reliability -Recognizing and exploiting commonality and variability across products

software process activities (4)

-Software specification, where customers and engineers define the software that is to be produced and the constraints on its operation. -Software development, where the software is designed and programmed. -Software validation, where the software is checked to ensure that it is what the customer requires. -Software evolution, where the software is modified to reflect changing customer and market requirements.

types of reusable software

-Stand-alone application systems (sometimes called COTS) that are configured for use in a particular environment. -Collections of objects that are developed as a package to be integrated with a component framework such as .NET, J2EE, Django, Spark, Symfony. -Web services that are developed according to service standards and which are available for remote invocation.

differences between buildings and software

-We know a lot about buildings, much less about software -The nature of software is different from that of building architecture -Software is much more changeable than physical materials -The two "construction industries" are very different -Software deployment has no counterpart in building architecture -Software is a machine; a building is not

test-driven development

-Writing tests before code clarifies the requirements to be implemented. -Tests are written as programs rather than data so that they can be executed automatically. The test includes a check that it has executed correctly. --Usually relies on a testing framework such as Junit. -All previous and new tests are run automatically when new functionality is added, thus checking that the new functionality has not introduced errors.

software process

A structured set of activities required to develop a software system. Specification - defining what the system should do; Design and implementation - defining the organization of the system and implementing the system; Validation - checking that it does what the customer wants; Evolution - changing the system in response to changing customer needs. A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.

requirements engineering process (software specification)

The process of establishing what services are required and the constraints on the system's operation and development. • Requirements elicitation and analysis -What do the system stakeholders require or expect from the system? • Requirements specification -Defining the requirements in detail • Requirements validation -Checking the validity of the requirements

software process descriptions

Capturing activities such as specifying a data model, designing a user interface, etc. and the ordering of these activities. Products - the outcomes of a process activity; Roles - reflect the responsibilities of the people involved in the process; Pre- and post-conditions - statements that are true before and after a process activity has been enacted or a product produced.

architectural configuration

Components and connectors are composed in a specific way in a given system's architecture to accomplish that system's objective -An architectural configuration, or topology, is a set of specific associations between the components and connectors of a software system's architecture

software

Computer programs and associated documentation Often referred to as "artifacts" Software products may be: Generic - developed to be sold to a range of different customers; The specification of what the software should do is owned by the software developer and decisions on software change are made by the developer. Custom - developed for a single customer according to the customer's specification; The specification of what the software should do is owned by the customer for the software and they make decisions on software changes that are required.

software engineering vs computer science

Computer science - concerned with theory and fundamentals Software engineering - concerned with the practicalities of developing and delivering useful software Computer science theories are currently insufficient to act as a complete underpinning for software engineering

Rationale for the code of ethics

Computers have a central and growing role in commerce, industry, government, medicine, education, entertainment and society at large. Software engineers are those who contribute by direct participation or by teaching, to the analysis, specification, design, development, certification, maintenance and testing of software systems. Because of their roles in developing software systems, software engineers have significant opportunities to do good or cause harm, to enable others to do good or cause harm, or to influence others to do good or cause harm. To ensure, as much as possible, that their efforts will be used for good, software engineers must commit themselves to making software engineering a beneficial and respected profession.

key challenges of software engineering (3)

Coping with: Legacy systems: Old, valuable systems must be maintained and updated Heterogeneity: Systems are distributed and include a mix of hardware and software Delivery: There is increasing pressure for faster delivery of software

Intellectual property rights

Engineers should be aware of local laws governing the use of intellectual property such as patents, copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected.

Confidentiality

Engineers should normally respect the confidentiality of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed.

Competence

Engineers should not misrepresent their level of competence. They should not knowingly accept work which is outwith their competence.

difficulties

Few guiding scientific principles Few universally applicable methods As much managerial / psychological / sociological as technological

Integration and configuration

The system is assembled from existing configurable components. May be plan-driven or agile. -Based on software reuse where systems are integrated from existing components or application systems COTS, GOTS, ROTS -Reused elements may be configured to adapt their behaviour and functionality to a user's requirements -Reuse is now the standard approach for building many types of business systems

architectural degradation/decay

Two related concepts: -Architectural drift - introduction of principal design decisions into a system's descriptive architecture that are not included in, encompassed by, or implied by the prescriptive architecture, but which do not violate any of the prescriptive architecture's design decisions -Architectural erosion - introduction of architectural design decisions into a system's descriptive architecture that violate its prescriptive architecture

architectural style

a named collection of architectural design decisions that --are applicable in a given development context --constrain architectural design decisions that are specific to a particular system within that context --elicit beneficial qualities in each resulting system reflect less domain specificity than architectural patterns

architectural pattern

a set of architectural design decisions that are applicable to a recurring design problem, and parameterized to account for different software development contexts in which that problem appears. --Many patterns are commonly used in practice

benefits of prototyping (5)

Improved system usability. A closer match to users' real needs. Improved design quality. Improved maintainability. Reduced development effort.

engineering

The application of scientific principles and methods to the construction of useful structures & machines

extreme programming practices (10)

-Incremental planning --Requirements are recorded on story cards and the stories to be included in a release are determined by the time available and their relative priority. The developers break these stories into development 'Tasks'. -Small releases --The minimal useful set of functionality that provides business value is developed first. Releases of the system are frequent and incrementally add functionality to the first release. -Simple design --Enough design is carried out to meet the current requirements and no more. -Test-first development --An automated unit test framework is used to write tests for a new piece of functionality before that functionality itself is implemented. -Refactoring --All developers are expected to refactor the code continuously as soon as possible code improvements are found. This keeps the code simple and maintainable. -Pair programming --Developers work in pairs, checking each other's work and providing the support to always do a good job. -Collective ownership --The pairs of developers work on all areas of the system, so that no islands of expertise develop and all the developers take responsibility for all of the code. Anyone can change anything. -Continuous integration --As soon as the work on a task is complete, it is integrated into the whole system. After any such integration, all the unit tests in the system must pass. -Sustainable pace --Large amounts of overtime are not considered acceptable as the net effect is often to reduce code quality and medium term productivity -On-site customer --A representative of the end-user of the system (the customer) should be available full time for the use of the XP team. In an extreme programming process, the customer is a member of the development team and is responsible for bringing system requirements to the team for implementation.

pair programming

-Involves programmers working in pairs, developing code together. -This helps develop common ownership of code and spreads knowledge across the team. -Serves as an informal review process as each line of code is looked at by more than 1 person. -Encourages refactoring as the whole team can benefit from improving the system code. -Programmers sit together at the same computer to develop the software. -Pairs are created dynamically so that all team members work with each other during the development process. -The sharing of knowledge that happens during pair programming is very important as it reduces the overall risks to a project when team members leave. -Not necessarily inefficient: there is some evidence that suggests that a pair working together is more efficient than 2 programmers working separately.

disadvantages of incremental delivery

-Most systems require a set of basic facilities that are used by different parts of the system. --As requirements are not defined in detail until an increment is to be implemented, it can be hard to identify common facilities that are needed by all increments. -The essence of iterative processes is that the specification is developed in conjunction with the software. --However, this conflicts with the procurement model of many organizations, where the complete system specification is part of the system development contract.

other definitions of software architecture

-Perry and Wolf --Software Architecture = { Elements, Form, Rationale } what how why -Shaw and Garlan --Software architecture [is a level of design that] involves ---the description of elements from which systems are built, ---interactions among those elements, ---patterns that guide their composition, and ---constraints on these patterns. -Kruchten --Software architecture deals with the design and implementation of the high-level structure of software. --Architecture deals with abstraction, decomposition, composition, style, and aesthetics.

prescriptive vs descriptive architecture

-Prescriptive architecture captures design decisions made prior to the system's construction --It is the as-conceived or as-intended architecture -Descriptive architecture describes how the system has been built --It is the as-implemented or as-realized architecture

architectural evolution

-Prescriptive architecture is modified first, ideally -In practice, the system's implementation - i.e., the descriptive architecture - is often directly modified -Happens because of: --Developer sloppiness --Perception of short deadlines which prevent thinking through and documenting --Lack of documented prescriptive architecture --Need or desire for code optimizations --Inadequate techniques or tool support

agile method applicability

-Product development where a software company is developing a small or medium-sized product for sale. --Virtually all software products and apps are now developed using an agile approach -Custom system development within an organization --There is a clear commitment from the customer to become involved in the development process; --There are few external rules and regulations that affect the software.

agile development

-Program specification, design and implementation are inter-leaved -The system is developed as a series of versions or increments with stakeholders involved in version specification and evaluation -Frequent delivery of new versions for evaluation -Extensive tool support (e.g. automated testing tools) used to support development. -Minimal documentation - focus on working code The goal: -to reduce overheads in the software process (e.g. by limiting documentation); -to be able to respond quickly to changing requirements without excessive rework.

refactoring

-Programming team looks for possible software improvements and make these improvements even where there is no immediate need for them. -This improves the understandability of the software and so reduces the need for documentation. -Changes are easier to make because the code is well-structured and clear. -However, some changes require architecture refactoring and this is much more expensive. Examples: -Re-organization of a class hierarchy to remove duplicate code. -Tidying up and renaming attributes and methods to make them easier to understand. -The replacement of inline code with calls to methods that have been included in a program library.

incremental delivery

-Rather than deliver the system as a single delivery, the development and delivery are broken down into increments with each increment delivering part of the required functionality. -User requirements are prioritised and the highest priority requirements are included in early increments. -Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.

types of software applications (8)

-Stand-alone applications: These are application systems that run on a local computer, such as a PC. They include all necessary functionality and do not need to be connected to a network. -Interactive transaction-based applications: Applications that execute on a remote computer and are accessed by users from their own PCs or terminals. These include web applications such as e-commerce applications. -Embedded control systems: These are software control systems that control and manage hardware devices. Numerically, there are probably more embedded systems than any other type of system. -Batch processing systems: These are business systems that are designed to process data in large batches. They process large numbers of individual inputs to create corresponding outputs. -Entertainment systems: These are systems that are primarily for personal use and which are intended to entertain the user. -Systems for modeling and simulation: These are systems that are developed by scientists and engineers to model physical processes or situations, which include many, separate, interacting objects. -Data collection systems: These are systems that collect data from their environment using a set of sensors and send that data to other systems for processing. -Systems of systems: These are systems that are composed of a number of other software systems.

separation of concerns

-Subdivision of a problem into (hopefully) independent parts. -The difficulties arise when the issues are either actually or apparently intertwined. -Frequently involves many tradeoffs -Total independence of concepts may not be possible. --Key example from software architecture: separation of components (computation) from connectors (interaction)

coping with changing requirements

-System prototyping - a version of the system or part of the system is developed quickly to check the customer's requirements and the feasibility of design decisions. --This approach supports change anticipation. -Incremental delivery - system increments are delivered to the customer for comment and experimentation. --This supports both change avoidance and change tolerance.

software engineering fundamentals

-Systems should be developed using a managed and understood development process. Of course, different processes are used for different types of software. -Dependability and performance are important for all types of systems. -Understanding and managing the software specification and requirements (what the software should do) are important. -Where appropriate, you should reuse software that has already been developed rather than write new software.

internet software engineering

-The Web is now a platform for running application and organizations are increasingly developing web-based systems rather than local systems. -Web services allow application functionality to be accessed over the web. -Cloud computing is an approach to the provision of computer services where applications run remotely on the 'cloud'. -Users do not buy software buy pay according to use.

pros of incremental development

-The cost of accommodating changing customer requirements is reduced. -The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model. -It is easier to get customer feedback on the development work that has been done. -Customers can comment on demonstrations of the software and see how much has been implemented. -More rapid delivery and deployment of useful software to the customer is possible. -Customers are able to use and gain value from the software earlier than is possible with a waterfall process.

cons of incremental development

-The process is not visible. -Managers need regular deliverables to measure progress. If systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system. -System structure tends to degrade as new increments are added. -Unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. -Incorporating further software changes becomes increasingly difficult and costly.

customer involvement

-The role of the customer in the testing process is to help develop acceptance tests for the stories that are to be implemented in the next release of the system. -The customer who is part of the team writes tests as development proceeds. All new code is therefore validated to ensure that it is what the customer needs. -However, people adopting the customer role have limited time available and so cannot work full-time with the development team.

software architecture

-The set of principal design decisions about the system -The blueprint for a software system's construction and evolution -Design decisions encompass every facet of the system under development --Structure --Behavior --Interaction --Non-functional properties Addresses issues: -Essential software engineering difficulties -Unique characteristics of programming-in-the-large -Need for software reuse

system implementation

-The software is implemented either by developing a program or programs or by configuring a system. -Design and implementation are interleaved activities for most types of software system. -Programming is an individual activity with no standard process. -Debugging is the activity of finding program faults and correcting these faults.

common architectural styles (7)

-Traditional, language-influenced styles --Main program and subroutines --Object-oriented -Layered --Virtual machines --Client-server -Data-flow styles --Batch sequential --Pipe and filter -Shared memory --Blackboard --Rule based -Interpreter --Interpreter --Mobile code -Implicit invocation --Event-based --Publish-subscribe -Peer-to-peer

user stories

-User requirements are expressed as user stories or scenarios. --These are written on cards and the development team break them down into implementation tasks. --These tasks are the basis of schedule and cost estimates. --The customer chooses the stories for inclusion in the next release based on their priorities and the schedule estimates.

software validation

-Verification and validation (V & V) is intended to show that a system conforms to its specification and meets the requirements of the system customer. -Involves checking and review processes and system testing. -System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system. -Testing is the most commonly used V & V activity: component testing, system testing, acceptance testing

prototyping

A prototype is an initial version of a system used to demonstrate concepts and try out design options. --May be thrown away A prototype can be used in: -The requirements engineering process to help with requirements elicitation and validation; -In design processes to explore options and develop a UI design; -In the testing process to run back-to-back tests.

elements of software's architecture

A software system's architecture should be a composition and interplay of different elements: -Processing -Data, information, or state) -Interaction

software engineering

40 years old: NATO Conferences, Garmisch, Germany, October 7-11, 1968, Rome, Italy, October 27-31, 1969 Nowadays, everything depends on it (Computer science as the scientific basis) Development of software systems whose size/complexity warrants team(s) of engineers Scope - study of software process, development principles, techniques, and notations Goal - production of quality software, delivered on time, within budget, satisfying customers' requirements and users' needs Software engineering is an engineering discipline which is concerned with all aspects of software production Software engineers should adopt a systematic and organised approach to their work and use appropriate tools and techniques depending on: the problem to be solved, the development constraints, and the resources available A key software engineering "axiom" Better Cheaper <-- pick any two Faster

software connector

In complex systems, interaction may become more important and challenging than the functionality of the individual components -A software connector is an architectural building block tasked with effecting and regulating interactions among components --usually simple procedure calls or shared data accesses --more sophisticated and complex connectors are possible --typically provide application-independent interaction facilities

software project failure

Increasing system complexity: As new software engineering techniques help us to build larger, more complex systems, the demands change. Systems have to be built and delivered more quickly; larger, more complex systems are required; systems have to have new capabilities that were previously thought to be impossible. Failure to use software engineering methods: It is fairly easy to write computer programs without using software engineering methods and techniques. Many companies have drifted into software development as their products and services have evolved. They do not use software engineering methods in their everyday work. Consequently, their software is often more expensive and less reliable than it should be.

problems with waterfall model

Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process. Few business systems have stable requirements. The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites. In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work.

issues of professional responsibility (4)

Intellectual property rights Computer misuse Confidentiality Competence

Computer misuse

Software engineers should not use their technical skills to misuse other people's computers. Computer misuse ranges from relatively trivial (game playing on an employer's machine, say) to extremely serious (dissemination of viruses).

economic and management aspects

Software production = development + maintenance Maintenance costs > 60% of all development costs: 20% corrective, 30% adaptive, 50% perfective Quicker development is not always preferable: higher up-front costs may defray downstream costs, poorly designed/implemented software is a critical cost factor

Incremental development

Specification, development and validation are interleaved. May be plan-driven or agile.

Reuse-oriented software engineering

Stages: -Requirements specification -Software discovery and evaluation -Requirements refinement -Application system configuration -Component adaptation and integration Real software processes are inter-leaved sequences of technical, collaborative and managerial activities Overall goal of specifying, designing, implementing and testing a software system.

software design and implementation

The process of converting the system specification into an executable system. •Software design -a creative activity in which you identify software components and their relationships, based on a customer's requirements •Implementation -the process of realizing the design as a program The activities of design and implementation are closely related and may be inter-leaved.

ACM/IEEE Code of Ethics (8)

The Code contains eight Principles related to the behaviour of and decisions made by professional software engineers, including practitioners, educators, managers, supervisors and policy makers, as well as trainees and students of the profession: 1. PUBLIC - Software engineers shall act consistently with the public interest. 2. CLIENT AND EMPLOYER - Software engineers shall act in a manner that is in the best interests of their client and employer consistent with the public interest. 3. PRODUCT - Software engineers shall ensure that their products and related modifications meet the highest professional standards possible. 4. JUDGMENT - Software engineers shall maintain integrity and independence in their professional judgment. 5. MANAGEMENT - Software engineering managers and leaders shall subscribe to and promote an ethical approach to the management of software development and maintenance. 6. PROFESSION - Software engineers shall advance the integrity and reputation of the profession consistent with the public interest. 7. COLLEAGUES - Software engineers shall be fair to and supportive of their colleagues. 8. SELF - Software engineers shall participate in lifelong learning regarding the practice of their profession and shall promote an ethical approach to the practice of the profession.

state-logic-display

three-tiered pattern used for --Business applications --Multi-player games --Web-based applications

agile processes

planning is incremental and it is easier to change the process to reflect changing customer requirements

plan-driven processes

processes where all of the process activities are planned in advance and progress is measured against this plan

software programming vs engineering

programming: Single developer "Toy" applications Short lifespan Single or few stakeholders Architect=Developer=Manager=Tester=Customer=User One-of-a-kind systems Built from scratch Minimal maintenance engineering: Teams of developers with multiple roles Complex systems Indefinite lifespan Numerous stakeholders Architect ≠ Developer ≠ Manager ≠ Tester ≠ Customer ≠ User System families Reuse to amortize costs Maintenance accounts for over 60% of overall development costs

Model-View-Controller (MVC)

separation between information, presentation, and user interaction -When a model object value changes, a notification is sent to the view and to the controller. --Thus, the view can update itself and the controller can modify the view if its logic so requires. -When handling input from the user the windowing system sends the user event to the controller. --If a change is required, the controller updates the model object. Model - encapsulation of information View - encapsulation of display choices (graphical display) Controller - encapsulation of interaction semantics (user-interface events)