需求分析第一章–软件过程

Topics

The nature of software development
System planning
Systems for three management levels
The software development lifecycle
Development models and methods
Problem statements for case studies (separate set of slides)

1.The nature of software development

1.1The essence of software development

The essence （本质）of software development：
defined by the issues inherent in the software itself： software is a product of a
creative act (not a result of a repetitive act of manufacturing)

software development invariants (constants):

complexity 软件规模，构件间依赖
conformity,(一致）与其他软件，硬件
changeability（需求）
invisibility.（源码）输出可见

本质不可改变

1.2The accidents of software development

‘Accidental difficulties’ (variables) due to software production practices ,amenable to human intervention

social system 由人造，被人用
adaptiveness (supportability) is the challenge
adaptiveness = understandability + maintainability + scalability
(extensibility)

意外不会增加软件产品的复杂性（？？？？）

意外因素

Stakeholders
Process
Modeling

Stakeholders

Customers (users and system owners)
Developers (analysts, designers, programmers）

Information systems are social systems developed by people (developers) for
people (customers)

Process

Defines activities and organizational procedures used in software production andmaintenance
A process model:

states an order for carrying out activities;
specifies what development artifacts are to be delivered and when;
assigns activities and artifacts to developers;
offers criteria for monitoring a project’s progress,for measuring the outcomes, and for planning future projects

Is not susceptible to standardization

ITIL, CMM and ISO 9000 are process standards（how to do）

Iterative and incremental process
– An iterative process is one that involves managing a stream of executable releases.
– An incremental process is one that involves the continuous integration of the system’s architecture to produce these releases, with each new release embodyingincremental improvements over the other.’ (RUP)
- examples:
  - the spiral model
  - the Rational Unified Process (RUP)
  - Model Driven Architecture (MDA)
  - the agile development process
  - aspect-oriented software development
    Iterative and incremental development
- must be planned and controlled, and
- must conform to a pre-defined architectural design framework (meta-architecture)
Capability maturity model
- 过程评估和改进，软件专用
ISO 9000 family of quality standards
- 质量管理和过程，只关注结果（质量），apply to any industry and all types of businesses
- premise：
  - if the process is right then the process outcome (product or service) will also be right
  - but… the ISO standards do not enforce or specify processes , the standards provide models of what must be accomplished, not how activities must be performed
ITIL framework( IT Infrastructure Library) IT 基础架构库
- IT as commodity ,solution ,service
- 用于IT service management，处理方案交付和管理
  - Efficient and effective use of the four Ps
    - people, processes, products (tools and technology) and partners (suppliers, vendors and outsourcing organizations)
- using ITIL solution management as a Continuous Service Improvement Programme (CSIP)
COBIT framework
- COBIT (Control OBjectives for Information and related Technology) is a compliance framework and addresses the control side of the solution management
- product standard （what to do）
- 针对高级IT经理，高级业务经理，不是软件开发者
- COBIT groups IT-related efforts into four domains:
  - Plan and Organize
  - Acquire and Implement,
  - Deliver and Support, and
  - Monitor

model

Modeling artifacts have to be

communicated (language) [‘The Unified Modeling Language (UML)]
documented (tools) [Computer-Assisted Software Engineering (CASE)]

UML

UML is independent of

any software development process
implementation technologies
just need object-oriented

The UML models can be categorized into thre groups:

State models :describe the static data structures
Behavior models : describe object collaborations
State change models: describe the allowed states for the system over time

CASE Process improvement

Process improvement is much more than the introduction of new tools, methods and techniques

may be bad for low level of process

CASE tool would always bring personal productivity and quality improvements to individual developers

1.3 Development or integration

Integration approaches

Information- and/or portal-oriented
Interface-oriented
Process-oriented

2.System planning

2.1 overview

System planning can be carried out in a number of different ways:

SWOT – Strengths, Weaknesses, Opportunities,Threats
VCM – Value Chain Model
BPR – Business Process Reengineering
Information System Architecture (ISA)

All system planning approaches have an important common denominator – they are concerned with effectiveness rather than efficiency
更关心效果（做正确的事）而不是效率（做事正确）

2.2 SWTO

s :strong,w :weak,o:opportunites,t:threat
from top to down

2.3 VCM(Value Chain Model）

analyzing the full chain of activities in an organization – from raw materials to final products
The question is: which value chain configurations will yield the greatest competitive advantage?

Organizational functions are categorized into:

primary activities
- they create or add value to a final product
support activities
- they are essential but they do not enrich the product

2.4 BPR approach(Business Process Reengineering)

base promise :organizations must reinvent themselves and abandon the functional decomposition, hierarchical structures and operational principles that they are now using
- Most contemporary organizations are structured in vertical units focused on functions, products or regions
- No one employee or department is responsible for a business process which is defined as ‘. . . a collection of activities that takes one or more kinds of input and creates an output that is of value to the customer’
- ‘The most visible difference between a process enterprise and a traditional organization is the existence of process owners
The main objective of BPR is to radically redesign business processes in an organization (hence, process redesign)
- The major hurdle lies in the need to embed a horizontal process
  in a traditional vertical management structure
- BPR initiative requires changing the organization around the
  development teams as the primary organizational units
- These teams are responsible for one or more end-to-end business
  processes

2.5 ISA approach (Information Systems Architecture)

buttom -up
The ISA framework is represented as a table of thirty cells organized into five rows (labeled 1 through 5) and six columns (labeled A through F)
- Rows represent the different perspectives used in the construction of a complex engineering product, such as an information system , five major ‘players in the game’
- Columns represent the six different descriptions or architectural models that each of the participants engages with

\	事由什么构成(数据)	业务过程	处理业务的构建位置	用户	事件和状态	企业动机
规划者(确定范围)
所有者(概念模型)
设计者(物理模型)
建造者(技术解决方案)
承包者(系统构件)

3 Systems for three management levels

3.1overview

strategic
tactical
operational

在这里插入图片描述

3.2 Transactional processing systems

Transaction – a logical unit of work that accomplishes a particular business task and guarantees the integrity of the database after the task completes
Database technology
Concurrency control
- Recovery
- Business logic (vs application/control logic)
- Security

3.3 Analytical processing systems

Analysis of pre-existing historical data to facilitate decision making
Data warehouse technology(数据仓库）
- Summarizing
- Packaging
- Partitioning
Data marts（数据市场）
Data webhouse

3.4Knowledge processing systems

Knowledge management – to help organizations discover, organize, distribute and apply the knowledge encoded in information systems

Data mining
- Association
- Classification
- Clustering
AI techniques ,predictive rather than retrospective models

4The software development lifecycle

4.1overview

The lifecycle identifies:

the applied modeling approach
the exact phases along which the software product is transformed – from initial inception to phasing it out
the method (methodology) and associated development process

4.2 Development approach

Software has become much more interactive

structured approach （1980）
- based on DFD(data flow diagram) ,ERD,
- process is centric
- non iterative and incremental
- inflexible
- does not support the reuse
Object-oriented approach(1990)
- Data-centric
- Matches the event-driven programming demanded by interactive GUI-based applications
Problems related to OO development
- The semantic gap between the object-oriented modeling artifacts and the implementation of the data-centric artifacts with relational database technology can be significant
- Project management is more difficult
- Object solutions are significantly more complex than old-style structured systems

4.3 Lifecycle phases

Business Analysis
- functional and non-functional requirements
System Design
- architectural design
- detailed design
Implementation
- coding
- round-trip engineering
Integration and Deployment
Operation and Maintenance

Business analysis/requirements analysis

Activity of determining and specifying customer requirements
- business analyst determines requirements
- system analyst specifies (or models) requirements
Business analysis is linked to business process reengineering (BPR)

Requirements determination

Requirement – ‘a statement of a system service or constraint
Service statement
- a business rule that must be obeyed at all times(e.g. ‘fortnightly salaries are paid on Wednesdays’)
- a computation that the system must carry out(e.g. ‘calculate salesperson commission based on the sales in the last fortnight using a particular formula’)
Constraint statement
- a restriction on the system’s behavior(‘only direct managers can see the salary information of their staff’ )
- a restriction on the system’s development (‘we must use Sybase development tools’ )

Requirements specification

Begins when the developers start modeling the requirements using a particular method (such as UML,CASE tool )
Most important specification techniques
- class diagrams
- use case diagrams
the specification models should be independent from the hardware/software platform on which the system is to be deployed

Architectural design

The description of the system in terms of its modules (components)
Concerned with
- selection of a solution strategy
- to resolve client (user interface) and server (database) issues as well as any middleware needed to ‘glue’ client and server processes
- modularization of the system
- relatively independent from a solution strategy but the detailed design of components must conform to a selected client/server solution
  需求分割为模块

Detailed design

Description of the internal workings of each software component
Develops detailed algorithms and data structures for each component
Dependent on the underlying implementation platform
- client
- server
- middleware
  无coding

Implementation

结果是可运行代码，debug在这

Integration and deployment

Module integration（can take more time and effort than any one of the earlier lifecycle phases, including implementation）
Application integration
deployment

Operation and maintenance

Operation signifies change over from the existing business solution, whether in software or not
Operation signifies change over from the existing usiness solution, whether in software or not
- Housekeeping
- Adaptive maintenance
- Perfective maintenance

Phasing out would normally happen due to reasons that have little to do with the usefulness of the software

4.4 Activities spanning the lifecycle

Project planning
Metrics
Testing

Project planning

Activity of estimating the project’s deliverables, costs, time, risks, milestones,
and resource requirements
Typical constraints are time and money

Metrics

Measuring development time and effort
Metrics are usually discussed in the context of software quality and complexity

Testing

Test cases should be defined for each functional module (use case) described in the requirements document
Desktop testing by developers not sufficient
Methodical testing by Software Quality Assurance (SQA) group necessary
Requirements, specifications and any documents (including program source code) can be tested in formal reviews (so-called walkthroughs and inspections)
Execution-based testing:
- Testing to specs (black-box testing)
- Testing to code (white-box or glass-box testing)

5 Development models and methods

overview

-Has an associated process – iterative and incremental

Representative models for iterative and incremental development:
- the spiral model
- the IBM Rational Unified Process (RUP)
- Model Driven Architecture (MDA)
- agile software development
- aspect-oriented development

Spiral model