Information systems tools and techniques

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Information systems tools and techniques

• Computers in business

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Information systems modelling

• Modelling the IS environment is a central theme
  in systems development.
• A model can be described as an abstract
  representation of the real world.
• The analysis and design stages of the IS
  development process use modelling techniques to
  describe and understand how an information system
  will operate in reality.
• Business activity can be separated into three
  business processes
• decision-making processes
• information-based processes
• functional processes

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Information systems modelling

• The processes must be decomposed into their
  logical parts so that a conceptual model of IS
  can be constructed.
• The development aspects of systems analysis and
  systems design are concerned with two primary
  activities
• process modelling
• data modelling
• Process modelling seeks to represent the various
  processes that are found within IS
• Data modelling is concerned with understanding
  and documenting data which forms the body and
  content of the IS.
• Object-oriented development attempts to include
  processes and data within one model.

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Process modelling

• This technique attempts to decompose the range of
  processes and functions of an IS into more
  manageable and understandable parts- known as
  functional decomposition.
• A system process will usually have one (or more)
  of the following characteristics
• inputs and outputs
• control areas of the organisation
• involves decision-making
• The technique of decomposition will normally
  continue until the most elementary processes are
  identified
• Decomposition is a top-down approach to the
  analysis of business systems processes.

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Process decomposition
Business area 1
Process A
Process B
Process C
Process D
Process E
Process F
A business area known as business area 1 is
decomposed into three processes known as A, B and
C. Process C is further decomposed into
elementary processes known as D, E, and F.
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Data modelling

• Data modelling is concerned with data structures
  and the elements of data, rather than information
  systems processes.
• Important to separate out the physical data model
  from the logical data model, so that the data
  model is implementation independent.
• It should not matter what technology is used in
  building the IS, the logical model is not
  dependent on the prevailing technology. A
  logical data model can be transcribed across a
  range of information technologies and business
  environments.

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Data modelling

• Important technique in data modelling is entity
  modelling. The essence of entity modelling is to
  establish the relationship between data elements
  within a business organisation. An entity can be
  described as a a body or object such as customer,
  supplier or employee.
• A number of techniques in data modelling include
• entity-relationship diagrams (ERDs)
• entity life histories
• normalisation

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Process modelling tools and techniques

• Most widely tools and techniques used within
  process modelling are
• flowcharting
• data flow diagrams(DFD)
• structured English.
• Flowcharting shows the relationship between
  systems(or applications) within a business
  organisation. Flowcharts exist in two main
  forms
• system flowcharting
• program flowcharting
• System flowcharting can be separated into
• simplified systems flowcharts
• detailed systems flowcharts.

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Flowchart symbols
Multi-document
Process
File storage
Input/output
Connector
Manual input
Sub-routine
Direction flows
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Flowcharts

• Simplified systems flowcharts merely show the
  relationship between various systems processes
  within a business organisation.
• Detailed systems flowcharts show all the various
  documents, files and activities that impact on a
  particular systems process.
• Systems flowcharts document the sequence and
  integration of processes that occur within an
  information system, and data and information
  input and output is of paramount importance.

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Simplified systems flowchart
Customer
Update sales order
Sales order processing
Accounting
Customer order
Check stock
Finished goods stock control
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Detailed systems flowchart
Customer data
Customer payments
Enter on system
Customer file
Accounting system (update files and
journals) (compute balances)
Payment file
General ledger (balances)
Updated customer file
Updated payment file
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Flowcharts

• Program flowcharting is similar to systems
  flowcharting. It graphically documents the steps
  that are followed in a specific software program
  rather than systems flowcharts which depict an
  entire information system.
• Program flowcharts are drawn using 3 control
  structures for executing instructions, as
  follows
• Sequence structure A series of statements that
  are executed in the order which they appear. I.e
  statement B will follow statement A
• Selection structure A series of statements that
  test a condition, such as true or false,
  yes or no, on or off, 1 or 0.
  Depending on the results of the test, one or two
  alternative instructions will be executed.
• Iterative structure. A series of statements that
  repeats an instruction as long as the results of
  the condition are true. For example, statement B
  will be executed as long as condition X is always
  satisfied.

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Data flow diagrams (DFDs)

• DFDs emphasise the structured nature of data
  processes, and so assist in the logical system
  model - unlike flowcharts that design a system in
  terms of physical files.
• DFDs achieve complete separation between the
  logical and physical design of an information
  system.
• DFDs use a set of restricted symbols, shown below

Data flows
Data store
External entity
Process
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DFDs

• Data flow is represented by an arrow which points
  in or out of a data process it indicates that
  data is moving from one process to another
  process and the direction of the flow.
• Data processes indicate the tasks to be
  performed on the data flows. The process is an
  activity that transforms of alters the data in
  some way. Data processes usually split into
  three compartments, top, middle and bottom. The
  top contains a reference number for the process,
  the middle contains a description of the process,
  and the bottom information on where the process
  occurs.
• Data stores are where the data flows finally
  stop. A data store contains data from a process
  or stored data for retrieval to a process. The
  data store contains two compartments, one for a
  reference number, and one indicating the name of
  the data store.
• External data entities represents an external
  source or destination of data. External data
  entities are often referred to as data sources or
  data sinks.

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DFDs

• DFDs are constructed to visualise an IS at
  various decomposed levels of detail.
• The top level of symbolic representation is known
  as the context diagram (or level 0). This is a
  general and broad representation of an IS.
• Context diagram is broken down into level 1,
  level 2, level 3 until the absolute level of
  detail is reached, process known as levelling..
• The top level context diagram consists of the
  overall system represented by a single process
  box, which alludes to the external entities..

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Context diagram (level 0) for sales order
processing system
Sales order
Storehouse
Customer
Credit check
Sales order processing
requirements
Credit agency
Credit rating
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Level 1 DFD
Stock items
A1
2.2
2.1
Customer
Checking order (Validation of customer order)
A2
Stock levels
Valid order
Checking stock
order
Stock dept.
Sales dept.
Order instructions
Invalid order
2.3
Checking invalidity
Customer report
Records dept.
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Level 2 DFD (2.1 Checking order exploded)
Customer file
A3
2.1.2
2.1.1
Customer
Customer details
Calculating customer bonuses (buying goods)
Recording customer details (records)
A4
Bonus file
New details
order
Sales (B)
Sales (A)
Update report
2.1.3
Generating invoice and reports
Customer bill (invoice)
Sales (C)
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Structured English

• Structured English uses a restricted sub-set of
  natural language English to provide precise
  descriptions of process or procedure design.
• Using this approach plain English statements or
  pseudo-code describe the processing stages and
  logic of information systems.
• A number of rules underpin the use of Structured
  English are as follows
• Complex sentences and grammatical structures are
  broken dowm into logical parts
• Use of statements that contain a precise verb and
  object.
• Avoid all adjectives, adverbs and other words of
  vague meaning
• Ignore words and sentances that are irrelevant to
  the process
• Use unique terms to identify items of data within
  the process
• Consistently use data terms found within DFDs and
  associated data dictionaries

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Application specification

• Many commercial programs involve the automatic
  printing of cheques. A cheque is characterised by
  its date, the payee and the amount to be paid.
  The printing of cheques is complicated by the
  need to prevent unscrupulous individuals from
  altering the amount to be paid. This is usually
  accomplished by printing the amount in words as
  well as in figures. The course-work will simulate
  this activity by displaying images of a printed
  cheques on the screen.
• The details of each cheque are to be entered
  using an appropriate data entry form and
  validated according to the following criteria
• The date of the cheque is to be the current date
  or some time in the future.The payee must consist
  of no more than 22 characters.The amount of the
  cheque must be greater than or equal to 1 and
  strictly less than 100000.
• When the details are entered and validated the
  cheque is to be displayed on the screen in a
  format similar to the above. The user is then
  prompted to see if any more cheques are required.
  If the response is affirmative, the process is
  repeated, otherwise the program is to display the
  total amount of all cheques printed and then
  terminate.

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Pseudo-code

• Set cheques total amount to zero
• REPEAT
• Get a valid date
• Get the cheque amount from 1 to 100000
• Get the payee name
• Get the user to confirm that the details
  are correct
• If the details are correct then
• display the cheque
• add the amount of the cheque to the total amount
• Prompt the user if more cheques are to be
  entered
• UNTIL no more cheques are to be entered
• display the cheque total amount.