©Ian Sommerville 2006MSc module: Advanced Software Engineering Slide 1 COTS Reuse.

©Ian Sommerville 2006 MSc module: Advanced Software Engineering Slide 1

COTS Reuse


Objectives

To introduce the notion of COTS reuse and to discuss the different approaches to COTS reuse that may be adopted

To explain the benefits and problems of the different approaches to COTS reuse

To discuss the issues around the development of software by configuring and adapting COTS systems and components


Topics covered

COTS solution systems COTS integrated systems Construction by configuration Configuration issues and problems


Commercial Off-the-Shelf Systems (COTS)

COTS systems are complete application systems (not components of some larger system) that can be deployed and run as independent systems.

Reuse of COTS systems involves adapting and configuring these systems for a specific operational environment.

Examples• Develop Excel spreadsheets to support project costing• Configure a patient record system for a specific medical

practice


Requirements issues

The top-down process of identifying requirements then building a system to deliver these requirements does not work

Rather, requirements engineering is an iterative process• What is wanted by stakeholders?• What is available from existing systems?• What is available from the system that is chosen

Stakeholders expectations have to be managed• The delivered system may not provide them with what

they want


General benefits

Extensive functionality can be delivered more quickly and more cheaply than for applications that are specially developed for specific requirements

Systems should be more reliable because they are widely used and extensively tested

Businesses can focus on their core activity rather than concerning themselves with IT systems development

Technology updates may be simplified as operating platforms evolve


General problems

Choosing the right COTS system for a particular organisation can be difficult

There may be a lack of expertise available to support systems development

System evolution is controlled by the system vendor rather than the system buyer• New versions may include unwanted functionality; Required

functionality may not be included Source code is not available so buyers are reliant the

system vendor continuing to support the product Product documentation is often inadequate Difficult to estimate the costs and risks of system

configuration and integration


Commercial Off-the-Shelf Systems (COTS)

COTS-solution systems • Choose a generic system that has been developed

to deliver some business function and adapt that system to the needs of a particular organisation.

COTS-integrated systems • Develop a new system by choosing a number of

COTS systems and integrating these to deliver combined functionality. Additional software (glueware) is required to make these systems work together.


COTS solution systems

Domain-specific applications• Application systems that are designed to support a

particular business application• For example, an appointment management system for

dentists Generic applications

• Generic systems that can be used with a range of other applications

• For example, email clients or spreadsheets Enterprise Resource Planning (ERP) systems

• Generic business systems built around a shared database


Domain specific applications

Domain-specific applications are (usually) business systems that have been designed to support a particular business function• Document management• Payroll and salaries• Student record management• Event booking

Usually have a basis in a specific system which has been generalised for wider use

Systems incorporate assumptions made by the vendor about the domain of application• E.g. students will only be registered for a degree at one

university


Benefits

Designed for a specific application area so provide extensive, integrated functionality to support that area

A specific user community may be created to share knowledge of problems and how to use the system effectively

Usually designed to support information sharing


Problems

The assumptions made by the vendor may not hold for the user of the system• We shall see later a system that had problems because

it assumed that it would be used under a particular legal system

The process of use may not match user processes Systems may only be available on limited platforms Sometimes expensive Reliant on continuing support from a single vendor May be no or limited API for integration with other

systems


Generic applications

Generic applications are general-purpose systems such as Excel or e-mail clients. That is, they offer functionality that is likely to be useful in many different areas of work

They may be configured to create personal systems• Excel, especially, has very powerful configuration

features that allow application-oriented spreadsheets to be created

More commonly, generic applications are incorporated as part of COTS-integrated systems


Benefits

Usually cheap Widely used and tested so fairly reliable May already be licensed for use by the

organisation procuring the system May be supported on different platforms Users may already be familiar with their user

interface (e.g. if Word is used for text input) Incorporate extensive functionality so may be

used in a range of different application types


Problems

As the systems are designed for stand-alone use, the API may not be well-defined or documented• This causes difficulties in integration with other systems

Undocumented system features may be incompatible with or may conflict with other COTS systems

System versions on different platforms may not be completely compatible

Systems are regularly superceded by new versions which may be incompatible

The system vendor may not support older versions of the system


ERP systems

ERP systems are intended to provide support for all data and processes in an organisation in a single, integrated system

Most large companies have now adopted some form of ERP system

Everything is integrated around a single database Generally, ERP systems include a number of business-

focused modules (e.g. manufacturing, supply chain, human resources, etc.) that are integrated using a set of process workflows and business rules

Primarily used by large companies and organisations SAP and Oracle are the major vendors of ERP systems


Systems architecture

System database

Business rules

PurchasingSupply chain

Logistics CRM

Processes Processes Processes Processes


ERP systems development

Modules in an ERP system are large and complex and extensive configuration is needed to describe the processes and rules of a business

Configuration involves:• Selection of modules - what business activities should

be/can be integrated• Development of process workflows• Specification of schemas• Definition of business rules• Definition of input forms• Definition of output reports


Benefits

Integration across business functions. • Data from one function is visible to other functions

• Reduces data duplication Reduces the number of separate software

systems that have to be managed and maintained


Problems

Very complex to configure ERP systems - thousands of tables and reports may have to be defined

There may be a mismatch between the processes and rules supported by the ERP system and an organisation’s processes

Forces a standard way of working on businesses • Can therefore lose competitive edge because of better

processes than competitors Difficult to integrate with legacy systems


COTS integrated systems

This approach is used when there is no single COTS system that can provide the required functionality or where it is essential for a new system to integrate with existing organisational systems

An application is constructed by integrating COTS systems from different vendors

Middleware is used to support communications between these different systems


Solution vs integrated COTS

COTS solution systems

COTS integratedsystems

Single product that provides required functionality

Generic solution with standard processes

Focus is on configuration

System vendor is maintainer

System vendor provides infrastructure

Several heterogeneous products integrated to provide customised functionality

Flexible solutions for specific processes

Focus is on integration

System owner is maintainer

System owner provides infrastructure


E-procurement systemClientWeb browserE-mail systemServerE-commercesystemOrdering andinvoicing systemE-mail systemAdaptorAdaptor


COTS products reused

On the client, standard e-mail and web browsing programs are used.

On the server, an e-commerce platform has to be integrated with an existing ordering system which was part of an ERP system.• This involves writing an adaptor so that they can

exchange data.• An e-mail system is also integrated to generate e-

mail for clients. This also requires an adaptor to receive data from the ordering and invoicing system.


Benefits

Extends the functionality of existing systems Faster system development and deployment

• E.g. the e-procurement system was delivered in 9 months rather than the predicted 3 years

Infrastructure upgrades are provided by the system vendors • E.g. systems are updated for new releases of the

OS


Problems Architectural mismatch

• The architectural models of the different products may be incompatible e.g. they may use different event models. Middleware may have to be written to resolve this problem

Performance problems• Systems with acceptable performance as stand-alone

systems may not be as effective when combined with other systems

Problems of upgrade management• Different vendors may have different upgrade cycles

Security issues• The security features of the different systems may be

incompatible. Integration may only be possible by weakening security


Construction by Configuration: COTS application engineering


Construction by configuration (C-b-C)

Software development with reuse rarely means reusing domain abstractions without change.

The reusable abstractions have to be configured to adapt them to their local circumstances of use.

This can range from simple parameter setting through the definition of business rules to special purpose component development.

C-b-C also may also include configuring the process as well as configuring the software that is the way people work has to change to meet the demands of the software.


Reuse and configuration

Components and services are intended to be used with limited configuration. Here the adaptation and configuration is often in the ‘glue code’ used to link these entities.

System families are configured by adapting specified parts of the system code.

ERP systems and generic COTS, by contrast, are designed for configuration without access to the source code of the system.


COTS configuration

COTS solution systems are designed for configuration The systems have been designed to include generic

functionality and abstractions from the domain which are configured for each specific customer through configuration interfaces

Programming is therefore configuration programming rather than programming in a conventional language

Configuration programming can be a (very) long-term process• The current Spanish en-route air traffic control system

is being reconfigured for use in the UK. The process is anticipated to take 6 years.


Configuration

I use the term ‘configuration’ to cover both customisation and adapting software to a specific execution environment.

Adapting the system to reflect:• The specific needs of a customer (e.g. a hospital);• The requirements of a user or group of users (e.g.

maternity unit or physiotherapy or both);• Interaction with other systems;• The characteristics of the platform on which the

software executes.


Configuration activities

Selecting required functionality Defining a data model Defining business rules Defining workflows Defining external interactions Defining the user interface Defining reports produced Setting platform parameters Data re-engineering Re-defining business processes


A patient management system

We have followed the deployment of a patient management system (PIMS) for mental healthcare in Edinburgh, Scotland.

Based around a generic COTS-package developed for hospitals in England.

This was designed to be adapted for supporting different kinds of clinic including mental healthcare.

Scotland has its own legal system and laws and healthcare is a devolved responsibility. The Scottish Executive sets its own targets and priorities for healthcare.


Procurement issues

A major influence in choosing the particular COTS system was that it offered the opportunity for hospital managers (rather than clinical staff) to control how information was recorded.

The Executive placed a tight deadline on hospitals for reporting against a set of targets.

There was little time to carry out a detailed comparison of alternatives and this system had already been successfully deployed elsewhere.


Software engineering

Configuring the data model required for a particular set of clinics.• i.e. setting up information about conditions, treatments,

etc. Configuring the menus for the particular type of clinic

and the patient information that had to be recorded. Configuring the reports to be generated by the system. Configuring the rules that should be applied to the

system data.


Issues and problems

Objectives conflict• Management objective - provide reports against a set of

headings defined by the Executive.• Clinical objectives - record patient information according

to clinical classification. Invalid configuration assumptions

• The language for defining the rules of the system was not expressive enough to cover the requirements of Scots law regarding the forced detention of patients who were a danger to themselves or others.

Failure to configure the process• Local process differences meant that different clinics

recorded different information about patients.


The C-b-C process for COTS

There is often no clear distinction between specification, design and development.

Systems are rarely completely configured before being put into use. The configuration process continues as the system is integrated with operational processes

There can be extensive (uncontrolled) “user” configuration of the system.

It is often necessary to configure the expectations of system stakeholders.


Process differences

Two-stage system requirements process• Identify general requirements to chose a reusable

system;• Identify specific requirements from settings where the

system will be used. Co-design of process and software

• May be more active stakeholder involvement in the development process.

System testing is a problem. Good practices such as configuration management,

reviews, etc. are practically impossible to implement.


Choosing a COTS system

The decision on which COTS system to use is rarely a transparent process, based on a detailed analysis of the requirements in a specific setting.

Issues that affect the decision include:• Political issues;• Platform issues;• Cost and schedule issues;• Availability of expertise;• Prejudice!


Co-design

For C-b-C, separating requirements and development/deployment is unlikely to be successful.

Requirements compromises are essential because the stakeholder’s real needs need to be matched with what the system actually provides.

Configurability makes co-design, with stakeholder involvement in the design process, much easier.


System testing

Testing is a particular problem for COTS-based systems.

Systems are not designed for running automated test suites.

There is no specification that can serve as a basis for deriving tests.

Problems that arise are often a consequence of interactions between the process of use and the system rather than system failure.


System evolution

Handover process from consultants to local IT staff. Change of system ‘ownership’• Limited expertise with system - may be managers

rather than software engineers. Problems of change management exacerbated

because of the system configurability• Increasing system entropy as local configuration

changes are implemented. Evolution of underlying COTS system outside control

of system owners.


Configuration problems

Understanding the configuration possibilities• Knowing what can be configured is not easy, especially

if more than one product is included in the system Understanding how to configure a system

• Typically, configuration requires both business knowledge and technical knowledge

Predicting the consequences of configuration decisions• It is often difficult to understand how changing a

configuration will affect the use and behaviour of a system while it is in operation

Understanding how a system is configured


Multiple configuration possibilities

Ways in which MS Word can be configured (that I’m aware of)• Preferences screen• Customisation screen• Organiser screen• Definition of templates• Definition of styles• Definition of macros• Inclusion of add-ins (e.g. Endnote)


Understanding how to configure


Configuration predictability

If you change a program, it is generally possible to hypothesise how this will affect the behaviour of the executing system.

When you change a configuration, the relationship is less obvious.

Change becomes a process of ad hoc experimentation. Gurus evolve who can suggest what to do but who can’t explain why it should be done that way.


Understanding the configuration

Once a system has been configured, how can others understand the configuration.

Requirements/design/code traceability is difficult enough in conventional systems but much harder in COTS where:• Requirements are not properly documented as a result of the

co-design process;• Understanding requires knowledge of the COTS system +

knowledge of the configuration. Change costing and impact analysis is difficult

• E.g. in the healthcare system we looked at, it was originally estimated that changing menus would take a few days. It ended up taking several months.


Challenges for C-b-C

Establish methods, tools and techniques for system engineering• Discover/establish general principles for designing

systems for dependable configuration.• Define processes and standards for C-b-C• Design new methods and tools to support the

processes of C-b-C. Adapt supporting software engineering processes for

C-b-C.


Principles

The diversity of different approaches to C-b-C mean that identifying unifying principles across different systems is very difficult

Possible examples of principles• Principle of visibility - make configurations explicit?• Principle of low coupling - reduce dependencies across

configurations?• Principle of scalability - separate configuration of

system deployment from configuration of functionality?• Principle of localisation - localise volatile configuration

entities?


Methods, tools and techniques

Visualisation and analysis of configurations• There is a need for tools that allow engineers to

see the ‘configuration state’ of a system and to explore dependencies across that state

Configuration policy description• There is a wide gap between organisational policy

(esp. security policy) and the realisation of that policy as a configuration. Methods and tools are needed to bridge this gap and hence reduce configuration errors.


Processes for C-b-C

Requirements engineering• Separation of the essential and the accidental

• Essential elements used to select reusable systems• Accidental requirements subject to negotiation

• This will clearly affect procurement processes. Design and implementation

• How can configuration ‘designs’ be modelled? System testing

• Testing against an incomplete spec. is difficult• How can test coverage be assessed?


Supporting processes

Users may be partly responsible for parts of the configuration process. This causes major problems with supporting processes • Configuration management

• Existing tools are oriented to source code

• Change management• Can users be stopped from making ad hoc changes?

• Quality management• What does a ‘high-quality’ configuration mean?


Conclusions

Construction by configuration is a reality for modern business software development.

Political, technical and economic factors mean that this approach will be increasingly used for all types of system.

Our current ‘ad hoc’ approaches are not good enough - we need to adapt software engineering methods and techniques for this approach.


Key points

Reuse of COTS systems requires the business to adapt its requirements and processes to fit the assumptions in the system that is being reused

COTS solution systems are single domain specific or generic systems that are reused. Development involves configuration

COTS integrated systems involve several different COTS systems. Development involves both integration and configuration


Key points

Construction by configuration is an approach to software engineering that relies on configuring existing COTS systems

Existing software engineering methods have to be adapted for this approach to development

Key problems include visualising and analysing configurations, understanding configuration interactions and testing configured systems

©Ian Sommerville 2006MSc module: Advanced Software Engineering Slide 1 COTS Reuse.

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Transcript of ©Ian Sommerville 2006MSc module: Advanced Software Engineering Slide 1 COTS Reuse.