BABOK_Guide_v3_member_copy

Techniques
Data Flow Diagrams
Figure 10.13.2: Level 1 Diagram Yourdon Notation
External
Agent
Noun
Output Data
Noun
External
Agent
Noun
Input Data
Noun
Data
Process
Verb/Noun
Noun
Data
Process
Verb/Noun
Input Data
Noun
External
Agent
Noun
Data
Process
Verb/Noun
Transformed
Output Data
Data Store
Input Data
Noun
External
Agent
Noun
Further levels of the data flow diagram (level 2, level 3 and so forth) break down
the major processes from the level 1 diagram. Level 1 diagrams are useful to show
the internal partitioning of the work and the data that flows between the
partitions, as well as the stored data used by each of the partitions. Each of the
partitions can be further decomposed if needed. The externals remain the same
and additional flows and stores are defined.
Logical data flow diagrams represent the future or essential state—that is, what
transformations need to occur regardless of the current physical limitations.
Physical data flow diagrams model all of the data stores, printers, forms, devices,
and other manifestations of data. The physical diagram can show either the
current state or how it will be implemented.
Complimentary IIBA® Member Copy. Not for Distribution or Resale.
10.13.3 Elements
.1 Externals (Entity, Source, Sink)
An external (entity, source, sink) is a person, organization, automated system, or any
device capable of producing data or receiving data. An external is an object which is
outside of the system under analysis. Externals are the sources and/or destinations
(sinks) of the data. Each external must have at least one data flow going to or
coming from it. Externals are represented by using a noun inside a rectangle and are
found within context-level diagrams as well as lower levels of abstraction.
251