Structured Analysis (SAD)

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DATA FLOW DIAGRAMS
Depict the broadest possible overview of system inputs, processes, and outputs, which correspond to those of the general systems.
DATA FLOW DIAGRAMS
a structured analysis technique
DATA FLOW DIAGRAMS
through this, the systems analyst can put together a graphical representation of data processes throughout the organization. By using combinations of only four symbols, the system analyst can create a pictorial depiction of processes that will eventually provide solid system documentation.
1. Freedom from committing to the technical implementation of the system early.
2. Further understanding of the interrelatedness of systems and subsystems.
3. Communicating current system knowledge to users through data flow diagrams.
4. Analysis of a proposed system to determine if the necessary data and processed have defined.
The data flow approach has four chief advantages over narrative explanations of the way data move through the system: (4)
1. double square
2. arrow
3. rectangle with rounded corners
4. open-ended rectangle
Conventions/Four basic symbols are used to chart data movement on data flow diagrams:
double square
is used to depict an external entity that can send data to or receive data from the system.
external entity
just entity
external entity
is also called a source or destination of data and it is considered to be external to the system being described.
True
Each entity is labelled with an appropriate name.
True
Entities should be named with a noun.
True
The same entity may be used more than once on a given data flow diagram to avoid crossing data flow lines
arrow
shows movement of data from one point to another, with the head of the arrow pointing toward the data's destination.
parallel arrows.
Data flows occurring simultaneously can be depicted doing just that through the use of ___________
noun
Because an arrow represents data about a person, place, or thing, it should be described with a ____.
rectangle with rounded corners
is used to show the occurrence of a transforming process.
Processes
always denote a change in or transformation of data; hence, the data flow leaving a process is always labelled differently than the one entering it.
True
Assign the name of the whole system when naming a high-level process.
True
To name a major subsystem, use a name such as INVENTORY REPORTING SUBSYSTEM or INTERNET CUSTOMER FULFILLMENT SYSTEM.
verb-adjective-noun
Use a ___________________ format for detailed processes.
verb
describes the type of activity
noun
indicates what the major outcome of the process is
adjective
illustrate which specific output
True
A process must also be given a unique identifying number indicating its level in the diagram.
open-ended rectangle
represent a data store
data store symbol
is simply showing a depository for data that allows examination, addition, and retrieval of data.
data store
may represent a manual store, such as a filing cabinet, or a computerized file or database.
data store
represent a person, place, or thing they are named with a noun
True
Temporary data stores, such as scratch paper or a temporary computer file, are not included on the data flow diagram.
CONTEXT DIAGRAM
is the highest level in a data flow diagram and contains only one process, representing the entire system.
CONTEXT DIAGRAM
The process is given the number zero.
CONTEXT DIAGRAM
All external entities are shown as well as major data flow to and from them.
CONTEXT DIAGRAM
The diagram does not contain any data stores and is fairly simple to create, once the external entities and the data flow to and from them are known to analysts.
Diagram 0
is the explosion of the context diagram and may include up to nine processes
Diagram 0
Including more processes at this level will result in a cluttered diagram that is difficult to understand.
Diagram 0
Each process is numbered with an integer, generally starting from the upper left-hand corner of the diagram and working toward the lower right-hand corner.
Diagram 0
The major data stores of the system (representing master files) and all external entities are included
two-dimensional
a data flow diagram is __________ rather than linear, you may start at any point and work forward or backward through the diagram
Work backwards from an output data flow
This approach is easier if prototypes have been created.
CHILD DIAGRAMS
Each process on Diagram 0 may in turn be exploded to create a more detailed _________
parent process, child diagram.
The process on Diagram 0 that is exploded is called the _____________ and and the diagram that results is called the ______________.
vertical balancing
dictates that a child diagram cannot produce output or receive input that the parent process does not also produce or receive
CHILD DIAGRAMS
Entities are usually not shown
interface data flow
Data flow matches the parent flow is called
interface data flow
shown as an arrow from or into a blank area of the child diagram
CHILD DIAGRAMS
If the parent process has data flow connecting to a data store the child diagram may include the data store as well.
CHILD DIAGRAMS
may contain data stores not shown on the parent process.
True
Minor data flow, such as an error line, may be included on a child diagram but not on the parent.
primitive process
When process is not exploded it is said to be functionality primitive and is called
True
Data stores and entities may not be connected to each other; data stores and external entities must connect only with a process.
1. Connecting data stores and external entities directly to each other
2. Incorrectly labelling processes or data flow
3. Including more than nine processes
4. Omitting data flow
5. Creating unbalanced decomposition (or explosion) in child diagrams
6. Forgetting to include a data flow or pointing an arrow in the wrong direction
Common Errors: (6)
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