Tm354 - Unit 1.4

Modelling is a way of thinking about things and ideas in the ‘real world’.

A model, in terms of software development, is an abstract representation of a specification, a design or a system, from a particular point of view. In general, it is a simplification of reality, created in order to understand an aspect or viewpoint of the system in question.

• A way of understanding the problems involved.

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• An aid to communication among those involved, especially between the developer and the user, as part of some deliverable.

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• A component of the processes used in development activities such as analysis and design.

A ‘good model’ is an abstraction that allows those involved to concentrate on the essentials of a complex problem by excluding non-essential details while capturing those of interest.

There are two distinct kinds of rule:

• those that determine whether or not a diagram is legal – its syntax

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• those that define what a legal diagram means – its semantics.

When choosing a modelling language, it should be:

• sufficiently expressive

• easy to learn and use

• unambiguous

• widely used

• supported by suitable tools

No, a modelling language does not dictate how it should be used and it is up to a development process to define which notations are appropriate and how they should be used. With experience practitioners tend to pick and mix from different modelling languages and use the notations that are most appropriate to the task – most modelling languages do not provide notations for all types of tasks.

A standard modelling language helps when new people join a project – a common modelling language reduces the time needed to enable them to become productive team members. Also, when a modelling language is widely used, it is likely that project components will have been constructed using that language. This makes the software easier and cheaper to maintain.

No, because you will be interested in different aspects of a design at different times, and different models of your design will be built to reflect your interpretations of users’ needs.

A structural model describes the elements of the system and their relationships to other elements.

A behaviour model describes the behaviour of a system over a period of time.

Yes, the whole set of diagrams should contain the different aspects of a single software system, so they should not contradict one another. For example, there must be some consistency checking between the static and dynamic models. This can be automated by a suitable tool.

The Unified Process is an iterative and incremental development process for building enterprise systems based on an object-oriented approach, and using UML.

Timeboxing means that a (usually) short fixed period – for example, three to four weeks – is devoted to each development iteration.

​A UP project is organised into four major phases:

1. Inception. The business case is developed, together with an idea of the scope of the system and a rough estimate of the effort required.

2. Elaboration. The core of the system is developed in an iterative fashion. In this phase all major risks are addressed and resolved, most of the requirements are identified and dealt with, and a more realistic estimate of the effort required is made.

3. Construction. The final product is constructed, including the remaining lower-risk and easier elements of the system, again in an iterative fashion.

4. Transition. This includes beta testing and deploying the system.

• Domain modelling

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• Requirements

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• Analysis

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• Design

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• Implementation

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• Testing

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• Deployment

Domain modelling is concerned with gaining an understanding of the environment in which any system that is designed must operate.

During domain modelling, we produce the following artefacts:

• Initial problem statement – a description of the problem

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• Behaviour model – a description of the business processes and behaviour of the domain

• Business rules – constraints on the way the behaviour model operates

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• Glossary – definitions of relevant terms

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• Structural domain model – an initial structural model representing the concepts relevant to the domain.

The requirements phase is concerned with establishing and modelling what a software system must do.

The Volere template provides a disciplined way of recording requirements. The requirements phase comes after the domain modelling phase.

In the Analysis phase we start modelling the structure and behaviour of a software solution from a user’s perspective.

The design phase is concerned with making decisions concerning how a system will meet its specification.

During design you produce the following artefacts:

• Structural model, an updated version of the one produced during analysis but with its operations specified

• Behavioural models, showing how objects in the system will interact and behave internally, and also how functionality will be distributed across the system.

UP means unified process.

Its 2 initial phases are Inception and elaboration.

Inception is the initial planning phase of development.

Elaboration is the phase where most of the analysis and design occur.

A sprint is a timeboxed period of a maximum of a month where usable software is delivered.