EXAM2

chapter 9,18,3,23,22b, 13, COCOMO

Program evolution dynamics

The study of the process of system change.

What did Lehman and Belady propose after major empirical studies.

There were a number of ‘laws’ which applied to all systems as they evolved.

(more like sensible observations rather than laws. They are applicable to large systems devolved by large organizations. Perhaps less applicable in other cases.)

Lehman’s law

• Continuing change

• Increasing complexity

• Large program evolution

• Organizational stability

• Conservation of Familiarity

• Continuing growth

• Declining Quality

• Feedback system

What are Lehman’s laws applicable to?

Large, tailored systems developed by large organizations

(Confirmed in more recent work by Lehman on the FEAST project)

For applicability of Lehman’s laws it is not clear how they should be modified for?

• Shrink-wrapped software products

• Systems that incorporate a significant number of COTS components

• Small organizations

• Medium sized systems

Software maintenance

• Modifying a program after it has been put into use

• Does not normally involve major changes to the system’s architecture.

• Changes are implemented by modifying existing components and adding new components to the system

Types of maintenance

• To repair system faults (to correct deficiencies)

• To adapt software to a different operating environment (changing systems)

• To add or modify the system’s functionality (to satisfy new requirements)

Distribution of maintenance effort for Fault repair? (percentage)

17%

Distribution of maintenance effort for Software adaptation? (percentage)

18%

Distribution of maintenance effort for Functionality addition/modification? (percentage)

65%

Distributed systems architectures

• Client-server (services that are called on by clients) [servers that provide services are treated differently from clients that use them]

• Distributed object (no distinction between clients and servers)

Middleware

• Software that manages and supports different components of a distributed system

• Usually off-the-shelf rather then specially written software

• EX:
  transaction processing monitors;
  Data converters;
  Communication controllers.

Multiprocessor architectures

• Simplest distributed system model

• System composed of multiple processes that may execute on different processors

• model of large real-time systems

• may be pre-ordered or under the control of a dispatcher

Client-server architectures

• Application is modelled as a set of services that are provided servers and a set of clients that use them

• Clients know of servers but servers need not know clients

• Clients and servers are logical processes

• Mapping to the processes is not 1 : 1

Layered application architecture

• Presentation layer
  - concerned with presenting the results of the computation to system users with collecting user input.

• Application processing layer
  - concerned with providing application specific functionality

• Data management layer
  - concerned with managing system databases

Thin-client model

• all of the application processing and data management is carried out on the server. The client is simply responsible for running the presentation software

Fat-client model

• the server is only responsible for data management. The software on the client implements the application logic and the interactions with the system user

COBRA

• International standard for an Object Request Broker - middleware to manage communications between distributed objects

• Middleware for distributed computing is required at 2 levels:
  - at the logical communication level (allows objects on different computers to exchange data and control information)
  - at the component level (provides a basis for developing compatible components)

What structure is this?

COBRA

peer-to-peer architectures

• Systems are decentralized systems where computations may be carried out by any node in the network

• Overall system is designed to take advantage of the computational power and storage of a large number of networked computers

• Most p2p systems have been personal systems but there is increasing business use of this technology.

what is this a diagram of?

Web services

Services standards

• are based on agreed, XML -based standards so can be provided on any platform and written in any programming language

• Key standards
  - SOAP
  - WSDL
  - UDDI

SOAP stands for

Simple Object Access Protocol

WSDL stands for?

Web services Description Language

UDDI stands for?

Universal Description, Discovery, and integration

Agile Manifesto

• Individuals and interactions over processes and tools

• Working software over comprehensive documentation

• Customer collaboration over contract negotiation

• Responding to change over following a plan

Principles of agile methods

• Customer involvement

• Incremental delivery

• People not process

• Embrace change

• Maintain simplicity

Extreme programming practices

• Incremental Planning

• Small releases

• Simple design

• Test-first development

• Refactoring

Examples of refactoring

• 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

Test automation

Tests are written as executable components before the task is implemented

Pair programming

• Work in pairs, sitting together to develop code

• Helps develop common ownership of code and spreads knowledge across the team

• Serves an an informal review process as each line is looked at by more than 1 person

• Encourages refactoring

• similar to that of two people working independently

Software cost components

• Hardware and software cost

• Travel and training costs

• Effort costs

• Effort costs must take overheads into account

Software pricing factors

• Market opportunity

• Cost estimate uncertainty

• Contractual terms

• Requirements volatility

• Financial health

Productivity measures

• Size related: based on some output from the software process (lines of source code, object code instructions, etc.)

• Function-related: based on an estimate of the functionality of the delivered software.

Factors affecting productivity

• Application domain experience

• Process quality

• Project size

• Technology support

• Working environment

Estimation Techniques

• Algorithmic cost modelling

• Expert judgement

• Estimation by analogy

• Pricing to win

Motivation

• An important role of a manager is to motivate the people on a project

• It’s a complex issue but it has different types
  - Basic needs
  - Personal needs
  - Social needs

Human needs hierarchy (1 is the top 5 is the bottom)

1. Self-realization needs

2. Esteem needs

3. Social needs

4. Safety needs

5. Physiological needs

Personality types

• Needs hierarchy is an over-simplification

• Different personality types
  - Task-oriented
  - Self-oriented
  - Interaction-oriented

Task-oriented

The motivation for doing the work is the work itself

Self-oriented

The work is a means to an end which is the achievement of individual goals - e.g. to get rich, to play tennis, to travel etc.

Interaction-oriented

The principal motivation is the presence and actions of co-workers. People go to work because they like to go to work

Group organization

• Software engineering group sizes should be relatively small (< 8 members)

• Break big projects down into multiple smaller projects

• Small teams may be organized in an informal, democratic way

• Chief programmer teams try to make the most effective use of skills and experience

The people capability maturity model (five stages)

1. Initial

2. Repeatable

3. Defined

4. Managed

5. Optimizing

Security Dimensions

• Confidentiality

• Integrity

• Availability

Asset

Something of value which has to be protected

Attack

An exploitation of a system’s vulnerability

Control

A protective measure that reduces system’s vulnerability

Exposure

Possible loss or harm to a computing system

Threat

Circumstances that have potential to cause loss or harm.

Vulnerability

A weakness in a computer-based-system that may be exploited to cause loss or harm

Threat types

• Interception

• Interruption

• Modification

• Fabrication

Interception

allow attackers to gain access to an asset

Interruption

Allows an attacker to make part of the system unavailable

Modification

Allow attackers to tamper with a system asset

Fabrication

allows attackers to insert false information into a system

What is Cocomo

Constructive Cost Model

SLOC

Source Line of code
1. One logical line of code
2. Declarations are counted as SLOC
3. Comments are not counted as SLOC
4. Only count delivered code
5. SOURCE lines are created by the project staff

COCOMO Scale Drivers

• Precedentedness

• Development Flexibility

• Architecture/Risk resolution

• Team Cohesion

• Process Maturity

How many cost drivers does COCOMO have?

17

COCOMO Effort equation

= 2.94 EAF (KSLOC)^E

COCOMO Duration equation

= 3.67 (EFFORT)^SE

COCOMO Average Staff equation

= EFFORT/DURATION

Cloud Computing

Internet-based computing, where shared resources, software, and information are provided to computers and other devices on demand.

What services do cloud computing provide?

• Reliability

• Elasticity

• Affordability

Cloud Computing types

• Public

• Private

• Hybrid

Cloud Computing: Service Models

• Infrastructure-as-a-Service (Iaas)

• Platform-as-a-Service (PaaS)

• Software-as-a-Service (SaaS)

IaaS examples

• Amazon web service

• Google compute engine

• Azure

• Digital Ocean

PaaS examples

• Amazon web service

• Google compute engine

• Azure

• heroku

• Oracle

SaaS examples

• Office 365

• salesforce

• Netflix

• GoToMeeting

• Google Docs