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190 Part 3 • the analysis Process

Figure 7.10
Contents of Physical Data Flow Diagrams
Physical data flow diagrams
contain many items not found in • Manual processes
logical data flow diagrams. • Processes for adding, deleting, changing, and updating
records
• Data entry and verifying processes
• Validation processes for ensuring accurate data input
• Sequencing processes to rearrange the order of records
• Processes to produce every unique system output
• Intermediate data stores
• Actual file names used to store data
• Controls to signify completion of tasks or error conditions

physical means of doing business. For example, activities such as applying for a video store
membership card, checking out a DVD, and returning the DVD, would all occur whether the
store had an automated, manual, or hybrid system.

Developing Physical Data Flow Diagrams
After you develop the logical model of a new system, you may use it to create a physical data
flow diagram. The physical data flow diagram shows how the system will be constructed and
usually contains most, if not all, of the elements found in Figure 7.10. Just as logical data flow
diagrams have certain advantages, physical data flow diagrams have advantages, including:
1. Clarifying which processes are performed by humans (manual) and which are automated
2. Describing processes in more detail than logical DFDs
3. Sequencing processes that have to be done in a particular order
4. Identifying temporary data stores
5. Specifying actual names of files, database tables, and printouts
6. Adding controls to ensure the processes are done properly
Physical data flow diagrams are often more complex than logical data flow diagrams simply
because of the many data stores present in a system. The acronym CRUD is often used for create,
read, update, and delete, the activities that must be present in a system for each master file. A CRUD
matrix is a tool to represent where each of these processes occurs in a system. Figure 7.11 is a CRUD

Figure 7.11
Activity Customer Item Order Order Detail
A CRUD matrix for an Internet
storefront. This tool can be used Customer Logon R
to represent where each of four
processes (create, read, update, Item Inquiry R
and delete) occurs within a
system. Item Selection R C C

Order Checkout U U U R
Add Account C

Add Item C

Close Customer Account D
Remove Obsolete Item D

Change Customer Demographics RU

Change Customer Order RU RU RU CRUD
Order Inquiry R R R R