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7/28/2019 BUNDANG AIS chapter 9.pptx
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When unnormalized tables are splitand reduced to third normal form(3NF), they must then be linkedtogether by foreign keys.
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Keys in 1:1 Association
a true association exists between tables,
either (or both) primary keys may be
embedded as foreign keys in the related
tables
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Keys in 1:M Associations
a 1:M (or 1:0,M) association exists, theprimary key of the 1 side is embedded in the
table of the M side
To demonstrate, lets have
Business Rule 1.Each vendor supplies the firm with three (orless) different items of inventory but each item is supplied by
only one vendor.Business Rule 2.Each vendor supplies the firm with anynumber of inventory items but each item is supplied by onlyone vendor. (See figure 1)
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Figure 1-Applying the 1:M Key-Assignment Rule
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Figure 2-Reversing the 1:M Key-Assignment Rule
By contrast,
this shows
what the table
structure might
look like if the
designerreversed the
key-
assignment
rule byembedding the
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Keys in M:M Associations
to represent the M:M association betweentables, a link table needs to be created
M:M Business Rule.Each vendor supplies the
firm with any number of inventory items andeach item may be suppplied by any number ofvendors.
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The link table
(Part/Supplier
) contains theprimary keys
for the
records in the
Inventorytable (Part
Num) and the
related
Supplier table
(Supplier
Figure 3-Normalized Database Tables
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Update anomalies can generate
Insertion anomalies can result in
Deletion anomalies can cause the loss of accountingrecords and the
Accountants understand the data normalizationprocess and be able to determine whether a database isproperly normalized.
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It focuses on six primary phases of database design:
1. Identify entities.2. Construct data model showing entity associations.
3. Add primary keys and attributes to the model.
4. Normalize the data model and add foreign keys.
5. Construct the physical database.
6. Prepare the user views.
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identify the primary entities of the organization construct a data model of their relationships
Lets have an example with a
Proposal for a new purchasing system:
Identify the key operational features of the system.Search for the entities that underlie it.
.what to do
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Key features:
1. The purchasing agent reviews the inventorystatus report (Figure 4) for items that need to
be recorded.
2. The agent selects a supplier and prepares anonline purchase order.
example continuation
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Figure 4-Inventory Status Report
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3. The agent printsa copy of the
purchase order
(Figure 5a) andsends it to the
supplier.
Figure 5a-Purchase Order for Purchases System
example continuation
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4. The supplier shipsinventory to the
company. Upon its
arrival, the receiving
clerk inspects theinventory and prepares
an online receiving
report (Figure 5b). The
computer systemautomatically updates
the inventory records.
Figure 5b-Receiving Report for Purchases System
example continuation
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These are things aboutwhich the organizationwishes to capture data.
Two conditions need be met to pass the valid-entitytest:1. An entity must consist of two or more occurrences.
2. An entity must contribute at least one attributethat is not provided through other entities.
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Candidate entities are:
Purchasing Agent
Since we have no information on this point in our brief
description of the system, we will assume no specificdata are captured.
Receiving Clerk
We will assume that no clerk-specific data need be
captured that requires a dedicated table.
example continuation
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Inventory The Inventory entity meets both conditions. We can
logically assume that the attributes that define the
inventory entity are not provided through other tables.
Supplier
The description state that multiple vendors supply
inventory. No other entity would logically provide
supplier data.
example continuation
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Inventory Status ReportThis user view is derived entirely from existing
entities, and provides no additional data that requires a
separate entity.
Purchase Order
All transaction are unique events that must be captured
in the database. While some purchase order data
pertain to existing entities (Inventory and Supplier) in
the model, other attributes unique to the purchase
event will require one or more additional entities.
example continuation
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Receiving ReportIt is needed to capture transaction specific data that
require additional entities and must be modeled.
example continuation
Four entities passed:
Inventory
Supplier
Purchase order
Receiving report
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determine the associations between
entities
model associations into an ER (Entity
Relationship) diagram
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1) 0,M:M -association between the Purchase Order and
Inventory entities
2) M:M -association between the Inventory and Supplier
entities3) 1:0,M -association between the Supplier and the
Purchase Order entities
4) 1:1 -association between the Purchase Order and
Receiving Report entities
5) 0,M:M -association between the Receiving Report and
Inventory entities
example continuation
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Figure 6-Data a Model Showing Entity Associations
This
illustrat
es the
entityassocia
tion in
our
exampl
e.
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Add Primary Keys
assign primary keys to all entities in themodel to uniquely identify records
Add Attributes
every attribute should appear directly orindirectly in one or more user views
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Figure 7-Data Model Showing Primary Keys
This
present
s the
four
entities
in the
modelwith
primary
keys
assigned.
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Figure 8-Data Model Showing Keys and Attributes
The
attributes
assigned to
each entityare derived
from the
user views
of thePurchase
Order and
Receiving
Report and
from the
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remove repeating groups, partialand transitive dependencies
assign foreign keys to be able to linktables
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1. Repeating Group Data in Purchase Order
The attributes Part Number, Description, Order Quantity, and
Unit Cost are repeating group data.
2. Repeating Group Data in Receiving ReportThe attributes Part Number, Quantity Received, and
Condition Code are repeating groups in the Receiving Report
entity and moved to a entity called Rec Report Item Detail.
3. Transitive DependenciesThe Purchase Order and Receiving Report entities
contain attributes that are redundant with data in
Inventory and Supplier entities.
(see Figure 9)
example continuation
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Figure 9-Normalized Data Model
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create physical tables populate tables with data
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Figure 10-Normalized Tables
example continuation
This
illustrates
the 3NF
tablestructures
for the
database.The primary
and foreign
keys linkingthe tables
are
represented
by dottedlines.
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Figure 11-Users View-Purchase Order
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normalized tables should support allrequired views of system users
user views restrict users from haveaccess to unauthorized data
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Prepared by:
BSBA/MA-4A