System Development Techniques Individual Assignment

System Development Techniques

Diploma in Information Technology

Lesson 18

Learning outcomes After studying this chapter and the recommended reading, you should be able to:

• Explain the difference types of deployment (direct, parallel and phased)

Deployment

Deployment Approaches

• Deployment activities are highly interdependent with activities of the other disciplines.

• A system or subsystem can’t be deployed until it has been implemented and tested.

• If a system or subsystem is large and complex, it is typically deployed in multiple stages or versions, thus necessitating some formal method of configuration and change management.

Deployment Approaches

• Important issues to consider when planning deployment: – Incurring costs of operating both systems in parallel – Detecting and correcting errors in the new system – Potentially disrupting the company and IS operations – Training personnel and familiarizing customers with new

procedures

Deployment Approaches

• Different approaches to deployment represent different trade-offs among cost, complexity, and risk. The most commonly used deployment approaches are: – Direct deployment – Parallel deployment – Phased deployment

Direct Deployment

• Direct deployment (immediate cutover) – The new system is installed and quickly made operational,

and any overlapping systems are then turned off. – Both systems are concurrently operated for only a brief

time (typically a few days or weeks) while the new system is being installed and tested.

Direct Deployment

• Direct deployment (immediate cutover) – Advantage

• simplicity. • Old and new systems aren’t operated in parallel, • Fewer logistical issues to manage and fewer resources required.

– Disadvantage • Risk. • Older systems aren’t operated in parallel, • No backup in the event that the new system fails.

Parallel Deployment

• Parallel deployment – Old and new systems are operated for an extended period

of time (typically weeks or months). – Ideally, the old system continues to operate until the new

system has been thoroughly tested and determined to be error-free and ready to operate independently.

Parallel Deployment

• Parallel deployment – Advantage • Relatively low operational risk. • Any failure in the new system can be mitigated by

relying on the old system.

– Disadvantage • Cost - during the period of parallel operation, the

organization pays to operate both systems. • Full parallel operation may be impractical

– New and old system are using the same hardware.

Parallel Deployment

• Parallel deployment – A partial parallel operation may be employed if full parallel

operation is not possible – Possible modes of partial parallel operation :

• Processing only a subset of input data in one of the two systems. The subset could be determined by transaction type, geography, or sampling (e.g., every 10th transaction).

• Performing only a subset of processing functions (e.g., updating account history but not printing monthly bills).

• Performing a combination of data and processing function subsets.

Phased Deployment

• Phased deployment – the system is deployed in a series of steps or

phases. – Each phase adds components or functions to the

operational system. – During each phase, the system is tested to ensure

that it is ready for the next phase. – Phased deployment can be combined with parallel

deployment, particularly when the new system will take over the operation of multiple existing systems.

Phased Deployment

Phased Deployment

• The Phased deployment diagram shows – A phased deployment with direct and parallel deployment

of individual phases. – The new system replaces two existing systems. – The deployment is divided into three phases. The first

phase is a direct replacement of one of the existing systems.

– The second and third phases are different parts of a parallel deployment that replace the other existing system.

Phased Deployment

• Phased deployment – Advantage

• reduced risk because failure of a single phase is less problematic than failure of an entire system.

– Disadvantage • Cost and increased complexity. • Dividing the deployment into phases creates more activities and

milestones, thus making the entire process more complex. • However, each phase contains a smaller and more manageable set

of activities. • If the entire system is simply too big or complex to install at one

time, the reduced risks of phased deployment outweigh the cost and increased complexity

Summary

• If a system or subsystem is large and complex, it is typically deployed in multiple stages or versions, thus necessitating some formal method of configuration and change management.

• Different approaches to deployment represent different trade-offs among cost, complexity, and risk. The most commonly used deployment approaches are: – Direct deployment – Parallel deployment – Phased deployment

Read

Textbook:

• Satzinger, Robert & Stephen Chapter 14