Systems Development Lifecycle Implementation Verification Learning Objectives Identify

Systems Development Lifecycle Implementation & Verification

Learning Objectives Identify the different methods of system implementation, giving suitable uses, advantages and disadvantages of each. Identify the need for, and the different methods of, verification when entering data.

System Development Lifecycle

Implementation and Real / Live Data Testing Phase

Real / Live data Installing the new system will now test it with real or live data. n This will be the real test of the system which no amount of test data can do. There are several methods of ‘System Handover’.

Direct Changeover / Big Bang Scrap the old system and start using the new system immediately n Advantage: Fast implementation and no time is lost. Do not have expense of running two systems together and saves money in wages (see parallel running). n Disadvantage: Staff have no time to get used to the new system. Extremely difficult to revert back to the old system if the new system fails If things go wrong lose all data.

Parallel Running both the old system and the new system side by side until the new system has ‘proved itself’. n Advantages: No data is lost if new system is unsuccessful. Old system is immediately available if the new system fails. Staff have time to get used to the new system. n Disadvantages: Expensive as two sets of wages have to be paid and very slow implementation.

Phasing Old system is replaced in phases (one aspect is replaced by new system then second aspect and so on). Mixture of parallel running and direct Changeover/Big Bang. n n Advantage: Still have most of system if things go wrong. No expense of running two systems together. Disadvantage: If new system is unsuccessful lose some data and slow implementation.

Pilot running Implementing the whole system in just a part of the organisation or one microsystem in the whole organisation. Mixture of phased and parallel running. n Advantage: Still have most of system if things go wrong. No expense of running two complete systems together. n Disadvantage: If new system is unsuccessful lose some data and slow implementation.

Improvements Did the implementation reveal any problems? n Make the necessary changes and test again.

Verification Checks data is absolutely accurate. n Unlike validation which does not prevent mistakes unless they are invalid. Used to prevent errors occurring when data is copied from one medium to another. n e. g. paper to disk, disk to disk, memory to disk

Verification Methods 1. Double entry Typing the data in twice and computer compares the two copies. 2. Proofreading data Checking what is on the screen is the same as on the input document. Both are time consuming and costly but necessary if data must be completely accurate.

Difference between Verification & Validation: n Checking that acceptable or valid has been entered. Verification n Checking versions of data have been entered identically/accurately from one medium to another e. g. paper to disk, disk to disk, memory to disk