Legacy systems overview DT211 4

Legacy System definition “Legacy system is deficiency in a system in terms of its suitability to the business, its Platform Suitability or application software quality, with the effect that the system’s asset value diminishes, as does its ease of operation, maintenance, migration or evolution.”

Common profile of legacy systems Applications that are old or considered “outdated” All or part of the system is vital to the running of the business; i.e. it is a mission critical system No time to shut down and replace Often Badly designed and not integrated into organisational information system(s), expensive to maintain Prevalent in area such as central government, transportation, energy and the financial sector

How does an I.S. change to become legacy system? Lack of Software quality: this includes areas like quality of code (goto statement) and different styles due to maintenance ; Lack of System suitability with the new business process and their systems; e.g. the company has developed a data warehouse. Lack of quality of design and the documentation of the design, especially important as a system is changes over the years.

Examples of lack of software quality –Style - e.g. introduction of structural programming in a program using GOTO’s, or change from structured to object-oriented, –Organisation of code- e.g. program written with input, processing and output sections - maintainer puts processing code into the input or output sections. –Functionality - e.g. adding code to make current obsolete, without removing obsolete code

Underlying platform Hardware –e.g. 16-bit to 32-bit –mainframe to PCs Operating system –fast changing Networking –E.g. lan, wan Data management system –architecture, use and scale –E.g. relational database to oo databases System suitability (compatibility)?

Legacy Effects –Asset value goes down decrease in mission criticality decreased reliability –Ease of operation goes down User satisfaction: system too slow Decrease in ease of testing and auditing due to lack of documentation… of system –Ease of migration / evolution declines Ease of use/integration with new technology Scalability –Ease of maintenance declines Increase cost of maintenance Availability of resources Program size and complexity Dependence on individuals who maintain it.

Choosing potential solutions The 4Rs portfolio matrix: -

Solution strategies Leave them alone: e.g. little business value –Note while they are “technically” legacy systems they would not be considered as “real” legacy systems, in relation to this module at least, as mission/business criticality is an essential element of legacy systems Deal with them gradually Implement change as a ‘big bang’ Open assessment or assessment towards a particular solution

Architecture Solutions The most appropriate “new” architecture needs to consider its suitability to the organisational mission, business process and the I.T. organisational environment and data management. Should you consider: –an Object oriented approach may enhance the mission and business processes may inhibit I.T. environment and data management –Bespoke (custom made) May be excellent for business process, I.T. organisation…, but can be expensive and slow to implement and may even find resistance to its implementation.

Legacy system data reuse: Since legacy systems by definition were/are mission critical their data is essential so it requires reuse. –Open Database Connectivity (ODBC) Reuse of data over networks and the internet but not suitable for non-integrated systems. –Data migration: the most ideal way to reuse the data however care is required to ensure correct transfer, transformation….; the migration could be to an operational DB or data warehouse

Legacy code reuse Vertical wrapping: part of the application is used. Other software provides it with inputs and outputs the results to the end user. Horizontal wrapping: replacing of the user interface/data layer and not replacing the rest of it. Application wrapping: entire system is enclosed in software which allows it to re-perform its core activities. (used if legacy system functions.. are essential or match that of the organisation); e.g. using new financial software that dealt with the introduction of the euro

Question What is a legacy system and discuss what you would need to take into account, both form a business and technical perspective, in order to decide if you would reuse it