Information systems in business

Order Description Systems Analysis & Design 2- Audit Trail- With an online system, it is possible for users to sign onto a system, alter data stored in the files and sign off again without leaving a visible clue as to what happened. Unless the analyst develops an audit trail, no such protection would exist. The audit trail permits tracing of any input record or process performed on a system back to its original source. One way of accomplishing this is by automatically maintaining a transaction log. The details of each transaction are recorded in a separate file on the system. The storage of these details is automatic and invisible to the users. Each transaction is also timed-stamped to tell when it occurred. ‘Sage’, well-known Accounting software has audit trail built in to enable tracing any transaction/activity. CASE (Computer-Aided Software Engineering) tools- These are software, which help the systems analyst and designer in the analysis, design and build phases of a software project. They provide tools for drawing diagrams such as entity relations and storing information about processes, entities and attributes. CASE tools are primarily used by professional developers and are intended to assist in managing the process of capturing requirements and converting these into design and program codes. CASE tools are based on a user graphically specifying a design using a diagram, such as an entity relationship diagram and this logical design is then converted into a physical database structure. CASE tools permit different approaches to the design technique such as data flow diagrams (see page 10). They are often supplied as part of a database package like ‘Oracle’ database. CASE tools were introduced as part of the need to engineer software products more methodically. Data Security- • Correctness of data input ? • Password protection ? • Data encryption (when transmitting data using data communications) ? • Periodic backups ? • Presence of an audit trail ? • Presence of a virus checker and firewall protection ? 1 (ISB Lecture - Week 11) System tools used:?- Program (logic) flowchart 2 - Systems flowchart?This is a symbolic representation of a system or series of procedures with each procedure shown in sequence. Systems flowcharts are a widely used to show a system with its procedures. Examples: 3 - DecisionTables?A decision table shows conditions and actions in a simplified manner. It enables one to think through a problem and present its solution in compact notation. It divides a problem into its logical segments to provide structural analysis. Purpose: to assemble and present complex decision logic in such a way that it’s meaning can be readily understood. Tax rate & insurance rate tables are forms of decision tables. Important values of decision tables: . 1- Compactnotation-Manypagesofacomputerprogramflowchartcanbe condensed into a single table. ? . 2- Easytomodifyprogram-Addingnewconditionsorchangingagiven decision will not require substantial reformulation. ? . 3- Ability to produce a machine language program codes. A translator converts the decision rules into a set of programming language codes without human intervention. ? . 4- Compatiblewithotherformsofdocumentation-decisiontablesarenot complete substitutes for program flowcharts and methods, but they complement and supplement various types of documentation. ? Limitations of decision tables- 4 Decision tables are logical and present a good way of analysing a problem. But they do have limitations; • The most serious problem is that they tell 'what to do', but do not tell when to do it. • Decision tables should be kept small if they are to be useful. They have the habit of growing exponentially with large problems. An example of a decision table; Assuming that discounts are given depending on the amount ordered, delivery within 50 mile radius and customer turnover exceeding £100,000, the discounts applied can be seen below under action entry columns; Taken from, Graham Curtis & David Cobham, Business Information Systems, Sixth Edition, Page 441. 5 Further Decision Table Examples- Example 1- Road Traffic Lights as a Decision Table Rules Condition Stub 1 2 3 4 5 6 7 8 1. red light on? Y Y Y Y N N N N 2. amber light on? Y Y N N Y Y N N 3. green light on? Y N Y N Y N Y N Action Stub 1. stop 2. go 3. proceed with caution Legal combinations: Red on, green on, amber on, red and amber on. Steps involved in setting up a decision table:?1- Write down the conditions under condition stub. 2- Working out the RULES;?Number of rules= 2 raised to the power of number of conditions. The 2 used is because there are two outcomes; Yes (Y) & No (N). With this example as there are 3 conditions, there will be 2^3 = 8 rules. The 8 rules show the maximum numbers of different arrangements (permutations) that are possible between 3 conditions. The method used makes it simple for us to work out all possible permutations. 3-?Divide the 8 rules by 2 =4. Write down 4 'Y's and 4 'N's for the first condition (first row of rules). Divide the 4 obtained from previous division by 2 to obtain 2. Write down 2 'Y's and 2 'N's for the second condition (second row of rules). Divide the 2 obtained from previous division by 2 to obtain 1. Write down 1'Y' and 1 'N' for the third and final condition. 4- Examine each rule starting from rule 1. Write 'X' (or Xs) for action(s) that will be taken under each rule. You will find that in a rule, when a condition has 'Y' or 'N', another condition may become irrelevant in the same rule. If so, then put a '-' against that condition in the rule column. See Below; 6 Rules Condition Stub 1 2 3 4 5 6 7 8 1. red light on? Y Y Y Y N N N N 2. amber light on? Y Y N N Y Y N N 3. green light on? - - - - - - Y N Action Stub 1. stop X X X X 2. go X 3. proceed with caution X X X 5- Create the summary table-?Rewrite the table with reduced number of rules (check for identical rules and reduce). See below; Summary Table Rules Condition Stub 1 2 3 4 5 1. red light on? Y Y N N N 2. amber light on? Y N Y N N 3. green light on? - - - Y N Action Stub 1. stop X X 2. go X 3. proceed with caution X X Example 2- Narrative Account of Customer Credit Control Process If an existing customer's current balance is less than or equal to zero, no statement is printed. If an existing customer's current balance is greater than zero, but less than his/her credit limit, no additional conditions are checked and a statement is printed. Where the current balance exceeds the credit limit by 10% or less, a statement is printed and a credit warning message is added to it. Current balance that exceed credit limit by more than 10% result in all further orders being rejected. Write process account of the above narrative using a limited entry decision table. Solution 1- Write down the conditions under Condition Stub?A condition will be in the form of a question (with an answer ‘Y’ or ‘N’ which will appear under RULES). 7 Important – Think through writing the conditions. Keep the number of conditions?low.?For example if you write ‘Is current balance excess >10% ?’, then you do not need to also include ‘Is current balance excess <= 10% ?’ as another condition. This is because both conditions are?considered through the rules (‘N’ for the first condition means ‘Y’ for the second condition automatically). Checking this simple example; Condition Stub Is A greater than (>) 10? Is A=10? Rules 1234 Y Y N N Y N Y N Clearly, rule number 4 (N,N) considers ‘A is less than (<) 10’ and therefore, there is no need to write all 3 conditions. Hope this is clear. 2- Work out the RULES- As explained in the previous example; Number of rules = 2 raised to the power of ‘ number of conditions’.?There are 3 conditions with this example. Therefore, the number of rules= 2^3 = 8 3- Construct the rules as with the previous example; Rules Condition Stub 1 2 3 4 5 6 7 8 1. current balance>0? Y Y Y Y N N N N 2. current balance>credit limit? Y Y N N Y Y N N 3. current balance exceeded >10%? Y N Y N Y N Y N Action Stub 1. reject all further orders 2. print statement 3. add credit warning 4. no additional checks 4- Examine each rule as explained in the previous example: Rules Condition Stub 1 2 3 4 5 6 7 8 1. current balance>0? Y Y Y Y N N N N 8 2. current balance>credit limit? Y Y N N - - - - 3. current balance exceeded >10%? Y N - - - - - - Action Stub 1. reject all further orders X 2. print statement X X X 3. add credit warning X 4. no additional checks X X X X X X Note: If condition 1 =N, conditions 2 and 3 are irrelevant. Thus rules 5,6, 7 & 8 are the same.?If condition 1= Y and condition 2= N, condition 3 is irrelevant. Thus rules 3 and 4 combine into one. Result: 8 rules are reduced to 4. Summary Table Rules Condition Stub 1 2 3 4 1. current balance>0? Y Y Y N 2. current balance>credit limit? Y Y N - 3. current balance exceeded >10%? Y N - - Action Stub 1. reject all further orders X 2. print statement X X X 3. add credit warning X 4. no additional checks X X - DecisionTree?A decision tree helps analysing decisions that should be made within the processing and the sequence in which they occur. It gives a graphical presentation of the various choices or decisions that are available. Decision trees are methods used to select the most appropriate option at each stage in a process. Many management decisions can be structured as decision trees where a selection of one choice leads on to others. An example; 9 For more decision tree diagrams, you may like to search using Google for ‘Decision tree picture examples’ - Dataflowdiagrams?A graphical tool used to describe and analyse the movement of data through a system (manual or automated). The changes that data undergoes as it passes through the system indicate the processes involved. As a result systems can be designed based on concentration on the data that will flow through the proposed system. Dfds are the central tool and the basis from which other components are developed.?Data flow analysis methods were developed and promoted simultaneously by two organisations: 1- Yourdon- a consulting and professional development firm. (Demarco, Weinberg, Page-Jones have all 10 used Yourdon's method.)?2- Gane and Sarson (McDonnell Douglas) Symbols used: YOURDEN?DATA FLOW PROCESS SOURCE/DESTINATION DATA STORE Examples: 1- GANE & SARSON DATA FLOW OR PROCESS SOURCE/DEST. DATA STORE 2- A high-level view (also known as context diagram) of an order processing system 11 Data flow diagrams at different levels- The levels of data flow diagrams correspond to the levels of detail that management and users will need in order to discuss sensibly the analyst’s understanding of processes. It is clearly a powerful communication tool. 1- Context – this level provides an overview of a system with its sources/destinations’ and data flows. 2- Levels 1, 2 & 3 12 (Further information on DFDs can be found in the recommended book listed on next page) Top-Down Method- This is based on the hierarchical view of systems. The systems development procedures follow a top-down sequence of breaking down high-level specifications of what the system must be into increasingly detailed logical models of what it should do followed by the details of how it should be constructed. Further reading: 13 Graham Curtis & David Cobham, Business Information Systems, Fourth/Fifth/Sixth Edition. Chapter 12 – Processing Analysis and Modelling (Fourth Edition- pages 418 – 449)?(Fifth Edition- pages 438 – 474)?(Sixth Edition- pages 422 – 458) 14