1. DSS & Warehousing Systems
Chapter 3
Efrem Mallach
Prepared by
Luvai Motiwalla
Irwin/McGraw-Hill
Copyright © 2000 by The McGraw-Hill Companies, Inc. All rights reserved.

2. Systems, Information Quality, And Models
Introduction
Information systems
Data flow diagrams
DSS as information systems
Information and information quality
Creating information from data
The affect of computers on information quality
Models

3. Introduction
What is a system? And what are the key characteristics of a system?
Discuss internal feedback and external feedback in a system
A system is a group of interactive components with a purpose. The key characteristics of a system are :
Group:-a system must consist of more than one item.
Interacting:- The components must be relating to each other.
Components:-the components must be of elementary items incapable of further subdivision.
Purpose:-Every system has a purpose of existence.
Every system has a boundary,if nothing crosses the boundary of the system in either direction, then that system is called a closed system, otherwise it is called a open system.Systems often incorporate feedback. Feedback is output from a system component that becomes, perhaps after additional processing input to a system component.
Systems that use feedback to adjust their outputs, based on how well the result of those outputs matches the desired result, are called closed loop systems. Those that do not use feedback are called open loop systems.
Feedback can be internal to a system or external to it. The functioning of an elevator can be considered as an internal feedback system. In a advertising program, since the customers are outside the advertising selection system,it can be considered as an external feedback.

4. Information Systems
What is the difference between an information system and a system in general?
Pages 88 and 89
What is the difference between an information system and a system in general?
An information system is a system whose purpose is to store, process and communicate information.
A general system is a system which does not necessarily involve information technology.

5. Data Flow Diagrams What is a data flow diagram?
What does a data flow diagram show and what doesn’t it show?
Pages90 and 91
A a data flow diagram is a popular way to describe and information system
A data flow diagram is a convenient and widely accepted way to record and communicate (1) the processes and data stores that comprise a system and (2) the information flows among them and between them and the outside world.Data flow diagrams do not however show the timing relationships among system activities, the conditions under which certain activities occur, or the reasons why they occur. For this reason they must be augmented by other system description methods.

6. DSS As Information Systems
How does a decision support system differ from an information system in general?
Pages92 to 94
A decision support system is a specific type of information system. If we know that an information system is a DSS, we can infer conclusions about it that do not apply to all types of information systems:
A DSS usually uses one or more data stores that provide information to support the decision.
The DSS does not update the databases that it uses as external information sources.
The DSS communicates with the decision maker. Depending on the situation, we may depict the decision maker as an external entity as an part of the system.
In all likelihood, the decision maker supplies the DSS with specific information defining the decision to be made within the general category of decisions with which the DSS can help.That information tells the DSS what data to extract from its data stores.

7. Information and Information Quality
Difference between data and information
Pages 94 to 95
Information is whatever reduces our uncertainty about something we didn’t know or wee unsure of. The more the information reduces our uncertainty, the more information we have.
Information is derived from data by comparing two data elements, by performing computations on several data elements, or by a combination of these.
Several data elements, suitably processed and placed in their business context, create useful information for decision making.

8. Creating Information From Data
The two fundamental operations involved in turning data into information.
Comparing one data element with another
Performing calculations on data
Page 95 and 96
Calculations and comparisons are two basic operations that computers or people do with data.
The information systems that provide the greatest value are those that link people and organizations via shared data.

9. The Affect of Computers on Information Quality – Cont’d
The eleven factors that define information quality, and the affects of computers:
1 Relevance
Pages97 to 119
Relevance- the degree to which it applies to the task being performed.Computers can provide so much information to their user that the relevance of the information is reduced.
Information is the basis for nearly every organizational decision. High quality information causes these decisions to be made correctly. Low quality information can cause them to be made incorrectly, harming the organization. The ability of information to contribute to the goals of the organization depends on the quality of that information, which can be described in terms eleven factors.

10. The Affect of Computers on Information Quality –Cont’d
2 Correctness
3 Accuracy
Correctness- whether or not the information matches reality. Computers can produce information only if their inputs are correct and the processing of those inputs has been specified correctly.
Accuracy-a measure of the difference, if any, between an information item and the reality it represents. Computers can introduce inaccuracy through computational processes.

11. The Affect of Computers on Information Quality –Cont’d
4 precision
5 Completeness
Precision- the potential accuracy conveyed by internal and external data representations. Computers allow high precision, but the underlying accuracy of the data does not always justify it.
Completeness- the inclusion of all relevant data in arriving at information. Whereas computers do not generally affect completeness directly, they may hide its absence

12. The Affect of Computers on Information Quality –Cont’d
6 Timeliness
7 Usability
Timeliness – includes two aspects: the availability of information in time for its intended use, and the accuracy of the information as of the time of that use. Computers can improve the timeliness of information, but the cost of their doing so must be weighed against the value.
Usability – the ease of using the information for its intended purpose. Computers can increase information usability by formatting it appropriately, but this can be overdone.

13. The Affect of Computers on Information Quality
8 Accessibility
9 conformity to expectations
Accessibility – the degree to which information is available to users when and where needed. Computers generally improve accessibility, but poor performance,a poor user interface, or obtrusive security procedures may impair it.
conformity to expectations – measure how closely the creation of an information item matches the expectations of the person or people who will use it. Ensuring that computer – derived information conforms to expectations raises concerns that do not arise with manually developed information.

14. The Affect of Computers on Information Quality
10 Consistency
11 Cost of information
Consistency – An information item based on data elements that refer to the same time frame, organizational entity and assumptions. The impact of computers on consistency depends on the degree to which system designers took this factor into account.
Cost of information – refers to both the cost of computers, networks and more, that are used to obtain that information, and the cost of the time users spend time working with that information. Cost can usually be traded off against other information quality factors

15. Models
What is a model?
Reasons to use computer models to support decision making.
Pages 119 to 120
A model is a simplified representation of a real system or object. Models are used in decision support systems to predict the outcome of decision choices we might make
One advantage of models is ease of access and manipulation than the real system whose behavior we want to study.
Second , it is easier to extract data from them and
Third, they generate results more quickly.
For a model to be useful we must be sure not to simplify the description of the real system so far that the usefulness of the model is lost.