introduction to information systems: whiteley palgrave chapter 20 structured system analysis and des

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design
Structured
System Analysis
and Design
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Structured System Analysis and Design
• Diagramming techniques used in this class of
  methods include
• Data Flow Diagram
• Logical Data Structure / ER Diagram
• Relational Data Analysis
• Entity Life History
• It is probably best to devote one lecture and one
  (or more) tutorial to each technique.
• I tend to use the black / white board, as opposed
  to slides, for this material but slides are
  provided for those who would prefer.

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD)
• The DFD, in the words of Avison and Fitzgerald
  (2003)
• enables the system to be partitioned (or
  structured) into independent units of a desirable
  size so that they, and thereby the system, can be
  more easily understood.
• The DFD shows
• the flows of the data from users (externals) into
  the system,
• the flows of the data within the system,
• the processing and the storage of that data,
• the flows of information out of the system to the
  users.

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD)
• The DFD is a hierarchy of diagrams consisting of
• Context diagram (conceptually level zero).
• The level-1 DFD.
• Level-2 and further levels if required.
• The context diagram represents the system as a
  single process.
• Level-1 decomposes that process into the main
  system processes.
• Each level-2 diagram gives further detail for a
  level-1 process.

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) External

An entity outside the system, typically a
person, which inputs data into the system and /
or receives data output by the system. The oval
symbol contains the name of the entity, e.g.
customer.  
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Process

• A task performed on the dataflow.
• The processing requirement is represented as an
  imperative statement, e.g. process order.
• The top line of the box contains
• The process number, e.g. 3 (or 3.2 on a level-2
  DFD), and
• The location where the process takes place, e.g
  warehouse.
•  

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Datastore

• A stationary dataflow.
• This could be standing data, e.g. customer data
  or it could be trans-actions awaiting further
  processing, e.g. allocated orders.
• The symbol contains
• A label, e.g. D3, and
• The name of the datastore.

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Dataflow

An arrowed line showing the flow of data from
externals, to processes, datastores and
eventually back out to externals. Labelled with
the attributes (data items) or a description,
e.g. order.
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Context Diagram

• Identify the external entities the people who
  put data into the system or who receive data from
  the system.
• Identify the external dataflows inputs to the
  system and outputs from the system.
• Combine the data flows with the externals to
  produce a Context Diagram

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Context Diagram

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Level-1

• Identify processing requirements the things the
  system does to the data.
• Identify the datastores data that is held
  (permanently or temporally).
• Putting these together with the externals and
  (external) dataflows we get the level 1 DFD

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Level-1

• For example, to process a bike rental we
• Read Bikes.
• Read Rates.
• Agree Rental
• Store Agreement.

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introduction to IS chapter 20structured SAD

• Data Flow
• Diagram
• Level-1

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Flow Diagram (DFD) Level-2
• (and further functional decomposition)

• Processes that are fully functionally decomposed
  are shown with an asterisk in the bottom right
  hand corner.
• Other processes need some further details and a
  level-2 (or level-n diagram is drawn.

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introduction to IS chapter 20structured SAD

• Data Flow
• Diagram
• Level-2

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Data Modelling (LDS / ER-Diagram)
• Data Analysis works out the underlying structure
  of the data that is processed and stored by the
  system.
• The data analysis leads onto the design of the
  database.
• Data analysis produces a diagram that is called
• Entity Relationship (ER) Diagram, or
• Logical Data Structure (LDS).
• There are many variations on the standard we
  will keep it simple!

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• ER Diagram (LDS) Entity

An entity is a thing of interest to the
system. We have to look for the underlying data
requirement, e.g. a project or a staff member
rather than currently used documents, e.g. a
timesheet.
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• ER Diagram (LDS) Relationship

An association between two entities that is of
importance to the system, e.g. the association
between a project and staff members (who form the
project team). We show cardinality on the
relationship by using crows feet (the three
pronged end).
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• ER Diagram (LDS) Cardinality

Cardinality - entity 1 is associated with many
(zero, one or more) occurrences of entity 2.
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• ER Diagram (LDS) First Cut

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• ER Diagram (LDS) Additional Rules
• Data modelling conventions do not allow
  many-to-manys and we resolve these by introducing
  a link entity.
• There is not a lot of point in a one-to-one and
  we can usually merge the two entities.
• We should name the relationships.
• We can indicate optionality in the relationship
  by making the optional end of the relationship a
  dotted line.

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introduction to IS chapter 20structured SAD

• ER-Diagram
• Final

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Relational Data Analysis
• Relational data analysis uses the input and
  output documents of the system to make sure that
• We have all the attributes for each entity,
• The data model is properly structured,
• A process we call normalisation.

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Relational Data Analysis
• There are four stages in normalisation
• Un-normalised form list all attributes and
  identify a key.
• First normal form identify any repeating groups
  of attributes.
• Second normal form identify any attributes that
  are dependent on only part of their key.
• Third normal form (TNF) identify any attributes
  that are not dependent on the entity to which
  they are currently assigned.

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introduction to IS chapter 20structured SAD
Un-normalised Form rental-no cust-name cust-tel da
te-out time-out exp-time-back exp-period act-time-
back act-period deposit-type class-code class-desc
bike-reg-no bike-model pay-prepaid pay-prepaid-to
t pay-actual pay-actual-tot

• Relational Data Analysis
• Un-Normalised Form
• List all the attributes used on the document.
• Identify a key (by underlining it).

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introduction to IS chapter 20structured SAD
UNF rental-no cust-name cust-tel date-out time-out
exp-time-back exp-period act-time-back act-period
deposit-type class-code class-desc bike-reg-no bi
ke-model pay-prepaid pay-prepaid-tot pay-actual pa
y-actual-tot
First Normal Form rental-no cust-name cust-tel dat
e-out time-out exp-time-back exp-period act-time-b
ack act-period deposit-type pay-prepaid-tot pay-ac
tual-tot rental-no bike-reg-no class-code class-d
esc bike-model pay-prepaid pay-actual

• Relational Data Analysis
• First Normal Form
• Identify repeating groups
• Separate as a new entity.
• Identify the key.

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introduction to IS chapter 20structured SAD
1NF rental-no cust-name cust-tel date-out time-out
exp-time-back exp-period act-time-back act-period
deposit-type pay-prepaid-tot pay-actual-tot rent
al-no bike-reg-no class-code class-desc bike-model
pay-prepaid pay-actual
Second Normal Form rental-no cust-name
cust-tel date-out time-out exp-time-back exp-per
iod act-time-back act-period deposit-type pay-prep
aid-tot pay-actual-tot rental-no bike-reg-no pay-
prepaid pay-actual bike-reg-no class-code class-d
esc bike-model

• Relational Data Analysis
• Second Normal Form
• Partial Key Dependencies
• Separate as a new entity.
• Identify the key.

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introduction to IS chapter 20structured SAD
2NF rental-no cust-name cust-tel date-out time-out
exp-time-back exp-period act-time-back act-period
deposit-type pay-prepaid-tot pay-actual-tot rent
al-no bike-reg-no pay-prepaid pay-actual bike-reg
-no class-code class-desc bike-model
Third Normal Form rental-no cust-name
date-out time-out exp-time-back exp-period act-t
ime-back act-period deposit-type pay-prepaid-tot p
ay-actual-tot rental-no bike-reg-no pay-prepaid pa
y-actual bike-reg-no class-code
bike-model cust-name cust-tel class-code class-d
esc

• Relational Data Analysis
• Third Normal Form
• Identify attributes that are not dependant on the
  entity they are assigned to.
• Separate as a new entity.
• Identify the key.
• Mark foreign key.

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Relational Data Analysis
• The same analysis is performed on all input and
  output forms used in the system.
• We then
• Merge the lists of attributes for each entity
  (relationships with the same key).
• Draw the ER Diagram

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Relational Data Analysis
• The ER Diagram for the Rental Agreement TNF is

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Entity Life History (ELH)
• The ELH cross checks the DFD and the ER diagram.
• There is an ELH for each entity on ER diagram.
• The diagram uses Jackson structures to show all
  the events, and the sequence of the events, that
  can affect that entity.
• Jackson structures provide three basic
  constructs sequence, selection and iteration
  (plus the quit / admit).

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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Entity Life History (ELH) Jackson Structures

Sequence A consists of B followed by C and that
is followed by D. For instance if A is a
waterfall lifecycle project it will have a
feasibility stage followed by analysis and then
program-ming stages.
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Entity Life History (ELH) Jackson Structures

Selection A consists of B or C. For
instance, using the example of a project, the
feasibility study could be accepted or rejected.
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Entity Life History (ELH) Jackson Structures

Iteration A consists of zero, one or more
instances of B. Again using the example of a
project, it could be shown as an iteration of
stages as opposed to a sequence of named stages.
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introduction to information systems whiteley /
palgrave chapter 20 structured system
analysis and design

• Entity Life History (ELH) Jackson Structures

Quit and Admit An extra construct added for
use in ELHs. It is in effect a go to from Q1 to
A1. It is a sort of get out of jail card and
should be used very sparingly.
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introduction to IS chapter 20structured SAD

• ELH
• First Cut

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introduction to IS chapter 20structured SAD

• ELH
• Second Cut