DEveloping Information systems

You must plan carefully before beginning:

Steps in information system design: called the life-cycle of an 
info. system

1.  Analyze needs for new system 
2.  Design the new systems
3.  Code or implement the new system
4.  Install the new system - get people using it
5.  Maintain the new system

Called a life cycle for 2 reasons. Like a living being, an 
information system has different stages it goes through. The 
process repeats itself when an existing system is replaced with 
a newer one.

Steps 1 through 4 may take a few months each. Step 5 may 
last for 2 or 3 years. During this period it may be necessary to 
make changes - the steps followed for the system as a whole 
are followed to institute the changes. At the end of the useful 
period of a system, there are enough problems that need to be 
fixed that it is better to design a new system that try to 
maintain the existing system.

Step 1.  Analyze user needs
1. Bring together a system development team consisting of 
systems analysts, managers and users of the system.
2.  Identify the problem areas. Determine the shortcomings of 
the existing system and new features that should be in the 
new system. - 
3.  Learn as much as possible about the operation of the 
existing system, so that you will be able to replicate the parts 
you wish to keep. Document the existing system by creating a 
data dictionary showing all data items stored in the system, 
their use and format. Use data flow diagrams to show how 
data flows through the existing system. Use structured English 
or pseucode to describe the processes carried out by the 
existing system. Systems analysts use CASE tools (Computer-
Aided Software Engineering) to help build the data flow 
diagrams and data dictionaries.

if quantityOnHand = 0 then
     Create a backOrder record
     Write backOrder record to backOrder file
else if quantityOnHand < OrderAmount then
     Perform fill_partial_order process
     Set QuantityOnHand to zero
     Create a backOrder record
     Write backOrder record to back order file
else if quantityOnHand > OrderAmount then
     perform fill_complete_order process
     deduct OrderAmount from QuantityonHand
if new QuantityOnHand <> old QuantityOnHand and 
   new QuantityOnHand < ReorderPoint then
         Create a new order record
         Write NewOrderRecord to NewOrders file
         Write date of new order and quantity to inventory 
record

4.  Determine system requirements for the new system 
(requirements specification document). The system 
requriements are a set of statements that describe measurable 
goals of the new system.

  a.  The system should be able to locate and ship an item that 
is in stock in any warehouse in the country to the customer 
within 48 hours.

b.  The system should determine the best outlet to ship from 
and the cheapest way to ship.

Analysts determine the system requirements by interviewing 
users and managers or throught the use of prototyping. A 
prorotype is a simple version of an information system that 
demonstrates selected features of the final system. The user 
tells the analyst what is good and bad about the prototype 
operation.

Step 2.   Design the new system


1.  Identify several (3 0r 4) alternative solutions. 
		Generally there may be more than 1 way to design 
a system. Some of the solutions might involve developing the 
sytem in-house using a programming langauge. Others might 
involve purchasing an off-the-shelf system that meets the 
user requirements, or customizing a software package that you 
purchase to meet your needs. Developing the system in house 
is the most time-consuming. There are application 
development tools that can speed the process. 

2.  Evaluate them and pick the best. 
		List the evaluation criteria and eliminate any 
solution not capable of performing the job. Then perform a 
costs-benefits analysis on the remaining solutions to find the 
best one.This means list the advantages (benefits) and 
disadvantages of all of them and determine the relative costs 
of implementing them. Pick the one that provides the best 
performance for the lowest cost.

3.  Purchase any required hardware or software needed for 
the development and installation of the new system. Send RFP 
(Requests for proposals) to possible vendors describing the 
problem and solution you wish to follow. Ask for equipment 
proposals that will meet the system requirements. When you 
decide on possible equipment configurations from different 
vendors, send out RFQ - Request for quotation.

4.  Develop applications specifications which describe exactly 
how the system should interface with the user, store data, 
process data, and format reports. This is documentation that 
describes the new system operation so a programmer can 
implement it. It may consist of the same information as for the 
documentation of the existing system (data flow diagrams, 
data dictionaries, and structured English descriptions of 
processes).

Step 3.   Code (construct) the system

1.  install any new hardware or software needed to code the 
system. This might be a new, more powerful computer. It 
might be a new programming language (for system to be 
coded in house), a new software package (if a package is to be 
customized in house), or an expert system shell (if expert 
system is to be built). 

2.  Create the new system following the process chosen in the 
design stage Building a system in house called software 
engineering; software customization - modifying or 
customizing a system; knowledge engineering - entering rules 
for an expert system in knowledge base using an expert 
system shell.

2.  Test the system to identify any errors and fix them. 
Provide it with multiple sets of test data designed to stress the 
system and observe whether it processes the test data 
correctly. If not, correct the errors in the system. 

Three phases of testing: unit testing- test each system unit 
separately to see that it performs as expected. Integration 
testing - see whether the units operate correctly when 
combined together into the complete system. System testing - 
test whether new system works with the rest of the 
information systems in the organization.

Step 4.  Install (Implement) the new system

1.  Train users to operate the new system. Show them how to 
perform their required tasks with the new system. Develop 
user or procedure manuals which detail the steps they should 
follow.

2.  Convert data in the old system so that it can be used in the 
new system. If the old system is a manual system, data will 
have to be scanned in or typed in by data entry operators. If 
the old system is also computerized, a program can be written 
to convert the data so it is in the acceptable format for the 
new system.

3.  Convert from the old system to the new system. 4 ways to 
do this. Direct conversion - simply pull the plug on the old 
system and switch over to the new one. Dangerous - new 
system may not work properly - can't fall back and use the 
old system.  Parallel conversion - run both systems 
simultaneously for awhile, comparing results to make sure 
new system is working properly. Costly - requires enough 
hardware to support both systems. Also, users must enter 
duplicate data during conversion process. Phased conversion - 
gradually shift over one module at a time from the old system 
to the new system. Complicated because modules of new 
system must be compatible with modules of old system. Pilot 
conversion - If an organization has multiple branches using 
the new system, try it out on just one branch first to make 
sure it works. When the bugs are out, shift the other branches 
over to the new system.

4.  Acceptance testing. After conversion, operate the new 
system for a specified period of time, carefuly observing its 
operation to see whether it meets its evaluation criteria and 
there are no problems. At the end of the period, either accept 
it or reject it.

Step 5  Maintain the system

Maintain the system, correcting errors or bugs that appear 
(initial phase of operation), or to bring it up to date because of 
changes in regulation, organizational structure, or procedures 
(middle phase of operation). Finally make changes required 
due to hardware or software upgrades (later stages of 
operation). Eventually it will become obsolete because of 
organizational or hardware/software changes or it will no 
longer be cost-effective to operate. Time to start the life cycle 
over again.