by Burleson Consulting
The Data Warehouse Development Life Cycle
The Structured Specification
In a traditional systems analysis, the DFD does not stand by itself.
Rather, the DFD is augmented by a data dictionary that describes all
of the data flows and files, and a set of process logic
specifications that describes how each process transforms data
flows. A process logic specification (sometimes called a mini-spec)
can be expressed as structured English, decision tress, or any of
the many other techniques used to describe how data flows are being
changed. Listing 3.1 shows a sample process logic specification
using structured English.
Listing 3.1 A Level 1 DFD process logic specification for the
Minispec for PLACE_ORDER:
IF total_amt > 1000
Check CREDIT_RATING in CUSTOMER
IF CREDIT_RATING = 'BAD' then reject order
ELSE Store ORDER RECORD
FOR (each item on the order)
-- compare QTY_ORDERED in ORDER with QTY_ON_HAND in ITEM
IF QTY_ON_HAND < QTY_ORDERED
Remove item from order
Prepare backorder slip
-- Add the item to the order
Subtract QTY_ORDERED from QTY_ON_HAND.
Move QTY_ORDERED to QTY in LINE_ITEM.
Store LINE_ITEM record.
In traditional systems analysis, data
dictionary definitions for all data items are normalized, or
grouped, into database entities, which become entity/relational
models in systems design. Eventually, the E/R models become
relational tables during system implementation. The identification
and grouping of data items constitutes the entities that will
establish the basic entity/relation model for the database engine.
For example, consider the interaction between the place_order
process and the data files in Figure 3.3. The process place_order
uses the data flow total_amnt to check the credit rating in the
customer file. It also uses qty_ordered to check the inventory level
for the item, then moves qty_ordered to the line_item record, and
finally stores this record in the file.
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