legacy systems
Download
Skip this Video
Download Presentation
Legacy Systems

Loading in 2 Seconds...

play fullscreen
1 / 13

Legacy Systems - PowerPoint PPT Presentation


  • 124 Views
  • Uploaded on

Legacy Systems. What is meant by a legacy system? What it is / what it is not Why is it critical to business operations? Function-oriented design Assessing legacy systems. discard it? maintain it? re-engineer it? replace it?. An actual business example.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Legacy Systems' - vine


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
legacy systems
Legacy Systems
  • What is meant by a legacy system?
  • What it is / what it is not
  • Why is it critical to business operations?
  • Function-oriented design
  • Assessing legacy systems
  • discard it?
  • maintain it?
  • re-engineer it?
  • replace it?

Ch.26 - Legacy Systems

an actual business example
An actual business example
  • From Fall, 1992 to Summer, 1996: Working on the TMS/AMS System for PECO Energy
  • TMS – Task Managements System
    • Tracking Labor and Materials for projects
  • AMS – Asset Management System
    • PC Based System that was re-written from a previous legacy system
      • Mainframe NOMAD Database

Ch.26 - Legacy Systems

historical perspective ca 1992
Historical Perspective (ca. 1992)
  • The only GUI environments were Windows 3.11, Macintosh OS’s, and IBM’s OS/2.
  • The only network lion-share leaders: Novell, Banyan
  • Computers of the day:
    • 20MB (up to 1GB for a server)
    • 386 or 486 processing
    • 640K Conventional memory (RAM)

Ch.26 - Legacy Systems

the legacy
The “legacy”
  • An IBM OS/2 platform. (still, not true GUI)
  • Used IBM’s OS/2 network solution
  • Loaded the network software high, so 604K was available for the system “in that session”

Ch.26 - Legacy Systems

from somerville p 582
From Somerville p. 582:
  • Replacing a legacy system is a risky strategy for a number of reasons:
  • There is rarely a complete specification of the legacy system.
      • OJT, User testing of specific code, etc.
  • Business processes and legacy systems are often entwined
      • For PECO: It was a necessary part of operations (it tracked hours spent on a job, billing for the job, materials, miscellaneous labor, and miscellaneous overhead.)
  • Business rules may be embedded in the software of the legacy system
      • The PECO way
  • There may be unexpected problems with the new development of software to replace a legacy system

Ch.26 - Legacy Systems

implementation
Implementation
  • Different parts of the system implemented by different parts of the team (Dynamic nature permitted me to add new reports to the reporting library)
  • Part or all of the system may be implemented using an obsolete programming language (Clipper 5.0)
  • System documentation is often inadequate or obsolete. (or non-existent)
  • Years of maintenance may have corrupted the system structure. (ad-hoc requests were rampant)

Ch.26 - Legacy Systems

implementation cont
Implementation (cont.)
  • The system may have been optimized for space utilization or execution speed (as previously outlined)
  • The data processed by the system may be maintained in different files that have incompatible structures (data subsets, flat files, etc.)
  • A potential work-around as TMS/AMS got bigger: divorce the two, as two separate programs
    • The thought was that this would minimize the 604K requirements; not at all!

Ch.26 - Legacy Systems

what made up the legacy
What made up the legacy?
  • As a legacy system, TMS needed to be networked, and was benchmarked at using 604K memory:
  • Written in:
    • Clipper 5.0 (95% Clipper, 5% C)
  • Database of choice:
    • dBASE
  • External Reporting:
    • Report Writer 5.0

Ch.26 - Legacy Systems

legacy system structures 26 1
Legacy System Structures (26.1)
  • System hardware (Legacy systems written for hardware systems not available anymore)
    • IBM PS/2 Series
  • Support software (Legacy systems may rely on supporting software)
    • RR and OS/2
  • Application software (The application relies on a series of interconnected programs)
    • Clipper & C, RR, dBASE

Ch.26 - Legacy Systems

legacy system structures 26 1 cont
Legacy System Structures (26.1) (cont.)
  • Application data (The data which are processed by the application system)
    • Terminal data entry
    • Files grew quickly, and wastefully
  • Business Process (The business objective)
    • Tracking the labor, materials and assets
  • Business policies and rules (How business was done at PECO)
    • Billing codes, constraints, overrides

Ch.26 - Legacy Systems

legacy system design 26 2
Legacy System Design (26.2)
  • Most are non- or pre-OO Development
    • (TMS tried to go OOP with class(y))
  • Conforms to a function-oriented design (broken down into reusable components)
    • this can cause problems: too many programmers dilute the code. Integrity is violated
    • it is only successful when information sharing is explicit

Ch.26 - Legacy Systems

legacy system assessment 26 3
Legacy System Assessment (26.3)
  • Organizations, which depend on these systems, must decide (realistically) on the course to follow on their system
  • Assessment:
    • Scrap the system completely
    • Continue maintaining the system
    • Transform the system in some way to improve its maintainability
    • Replace the system with a new system

Ch.26 - Legacy Systems

peco s solution
PECO’s Solution
  • Scrap the system?
    • Auditors (PECO & the subcontractors) needed the data
  • Continue maintaining the system?
    • The company was moving away from OS/2
  • Transform the system in some way to improve its maintainability?
    • Had been tried, unsuccessfully
  • Replace the system with a new system?
    • Spring 1997, a new team came in to re-write TMS using VBA (Visual Basic for Applications)

Ch.26 - Legacy Systems

ad