Chapter 7 Data Flow Diagramming Copyright 2016 McGraw-Hill
Chapter 7 Data Flow Diagramming Copyright 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Outline Learning objectives Nature and purpose of DFDs DFD symbols Leveling and balancing Database design Normal forms 7-2 Learning objectives
1) Explain the symbols and design considerations associated with DFDs. 2) Compare and contrast flowcharts and DFDs with regard to purpose, content, structure, and use in accounting information systems. 3) Discuss ways DFDs are used in AIS work. 4) Construct a leveled set of DFDs. 5) Design normalized database tables from a DFD. 7-3 Nature and purpose of DFDs Not as widely used as flowcharts in accounting practice Two main purposes Understanding a business process Understanding the relational database that
underlies the AIS Focus on data 7-4 DFD symbols external entity process data store data flow 7-5
DFD symbols 1.0 Take customer order customer order database customer order 7-6 Leveling and balancing Data flow diagrams are prepared in leveled sets. Each level reveals more detail than the
one before it. Levels must be balanced, which means that external entities and data flows at the boundary cannot disappear between levels. 7-7 Leveling and balancing Level names Context diagram Level Zero diagram Level One diagrams Level Two diagrams And so on. . . 7-8
Leveling and balancing Customer Context diagram Highest level view of the system Exactly one in a leveled set Exactly one process One or more external entities
No data stores Invoice Customer order 0 Order taking process 7-9 Leveling and balancing Customer
Level Zero diagram Exactly one in a leveled set More detail than the context diagram Preserve data flows at the boundary Invoice Customer order
1.0 Process customer order. 2.0 Bill customer. Processed customer order 7-10 Leveling and balancing Level One diagram
May be more than one in a leveled set More detail than the Level Zero diagram Each Level One focused on a single bubble from Level Zero Preserve data flows at the boundary See the example on the next slide, which explodes Process 1.0
(Process customer order) from the Level Zero diagram. 7-11 Leveling and balancing Processed customer order Customer Customer order 1.1 Verify
decision Customer database 7-12 Leveling and balancing Processes are decomposed (exploded) until they are primitive. Processes may be decomposed to different levels. Numbering conventions Level One diagram of Process 2.0: 2.1, 2.2 Level Two diagram of Process 1.2: 1.2.1, 1.2.2
7-13 Database design Objects Terminology Normal forms 7-14 Database design Objects: tables Every relational database must include at least one table. Most will include multiple tables Organization Fields (columns)
Records (rows) See the example on the next slide. 7-15 Database design Student table in design view Student table in datasheet view 7-16 Database design Objects: queries Sets of instructions that examine current data
in tables and / or other queries Output data according to the instructions Can include simple computations (e.g., total, average) See the example on the next slide 7-17 Database design Query in design view Query in datasheet view 7-18 Database design
Objects: forms Allow a user to interact with a database even if they know nothing about design and structure Two uses: data input, data lookup See the example on the next slide 7-19 Database design Form in design view Form in form view 7-20
Database design Objects: reports Well formatted output of a relational database Can be based on tables and / or queries Can incorporate simple calculations See the example on the next slide 7-21 Database design Report in report view (Design view not shown) 7-22
Database design Terminology Primary key: a field in a table that uniquely identifies every record in that table Foreign key: a primary key in one table that is included in another table for linking purposes Compound primary key: two or more fields in a table that together comprise its primary key 7-23 Database design Terminology Junction table A table that joins together two separate tables.
Required when the two separate tables have a many-tomany relationship Every student may enroll in many classes. Every class has many students. Named by joining the separate table names Student table Class table Student / class table This is the junction table. See the illustration on the next slide 7-24 Database design
Relationship grid 7-25 Database design Normal forms Table characteristics that ensure a relational database is organized as efficiently and effectively as possible Minimize space allocations Facilitate searches Establish relationships between tables 7-26 Database design
First normal form (1NF) Eliminates repeating groups Second normal form (2NF) Eliminates repeating groups Eliminates redundant data Third normal form (3NF) Eliminates repeating groups
Eliminates redundant data Eliminates columns not dependent on the primary key 7-27 Database design The next few slides show you how to start with a flat file (such as a spreadsheet) and create normalized database tables. With practice, youll be able to design normalized tables from scratch. The following example is drawn from the 23 January 2014 post on Dr. Hurts AIS blog.
7-28 Normal forms Student ID 1026 1053 1221 1270 1397 Courses Acc 343, Psy 200 Acc 343, Eng 117 Bus 281, Mat 146 Acc 343, Eng 117 Bus 281, Psy 200
This data array is a flat file comprising two fields and five records. It is not normalized, as the courses field includes repeating groups of data (i.e., two courses in one field). 7-29 Normal forms To put the array in 1NF, we need to eliminate repeating groups. Student ID 1026 1053 1221 1270 1397
Course 1 Prefix Number Acc 343 Acc 343 Bus 281 Acc 343 Bus 281 Course 2
Prefix Number Psy 200 Eng 117 Mat 146 Eng 117 Psy 200 This array, while not fully normalized, is closer to that state. Note that we could search for specific course prefixes and / or numbers more easily than in
the flat file. 7-30 Normal forms To put the data in 2NF, we need to eliminate redundant data. Student table Student ID 1026 1053 1221 1270 1397 Course table Prefix
Number Acc 343 Bus 281 Psy 200 Eng 117 Mat 146 Neither table has repeating groups or redundant data; however, were missing key information: which students are in which courses? 7-31
Normal forms Junction table Completes 2NF by marrying data from two other tables Requires a compound primary key Many-to-many relationship Each student can take many courses. Each course can have many students. Student / course table
Student ID Prefix Number 1026 Acc 343 1026 Psy 200 1053 Acc 343 1053 Eng 117 1221 Bus
281 1221 Mat 146 1270 Acc 343 1270 Eng 117 1397 Bus 281 1397 Psy 200
7-32 Normal forms To put the data in 3NF, we must ensure that each table contains only fields that give us more information about the primary key. Student table: last name, first name, area code, phone number Course table: course title, instructor, building, classroom, section number Student / course table: probably does not need any information beyond the primary keys of the two other tables 7-33
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