Database Design: Normalization

University of California, Berkeley

School of Information Management and Systems

SIMS 202: Information Organization and Retrieval

Review

Entity-Relationship Diagrams

Designing a database

Entities

Customer

Invoice

Employee

Inventory

Supplier

Account

Sales Rep

Parts

Functional areas

Ordering

Inventory

Supplies

Shipping

Personnel

Payroll

We will concentrate on Ordering and Inventory

Ordering Normalization

ER Model

Mapping to a Relational Model

Each entity in the ER Diagram becomes a relation.

A properly normalized ER diagram will indicate where intersection relations for many-to-many mappings are needed.

Relationships are indicated by common columns (or domains) in tables that are related.

We will examine the tables for the Acme Widget Company derived from the ER diagram

Employee

Sales-Rep

Customer

Invoice

Line-Item

Part

Joins

Today

Normalization

Effectiveness and Efficiency criteria for database designs

Advantages and failings of DBMS technology

Normalization

Normalization theory is based on the observation that relations with certain properties are more effective in inserting, updating and deleting data than other sets of relations containing the same data

Normalization is a multi-step process beginning with an "unnormalized" relation

Hospital example from Atre, S. Data Base: Structured Techniques for Design, Performance, and Management.

Normal Forms

First Normal Form (1NF)

Second Normal Form (2NF)

Third Normal Form (3NF)

Boyce-Codd Normal Form (BCNF)

Fourth Normal Form (4NF)

Fifth Normal Form (5NF)

Normalization

Unnormalized Relations

First step in normalization is to convert the data into a two-dimensional table

In unnormalized relations data can repeat within a column

Unnormalized Relation

First Normal Form

To move to First Normal Form a relation must contain only atomic values at each row and column.

No repeating groups

A column or set of columns is called a Candidate Key when its values can uniquely identify the row in the relation.

First Normal Form

1NF Storage Anomalies

Insertion: A new patient has not yet undergone surgery -- hence no surgeon # -- Since surgeon # is part of the key we can’t insert.

Insertion: If a surgeon is newly hired and hasn’t operated yet -- there will be no way to include that person in the database.

Update: If a patient comes in for a new procedure, and has moved, we need to change multiple address entries.

Deletion (type 1): Deleting a patient record may also delete all info about a surgeon.

Deletion (type 2): When there are functional dependencies (like side effects and drug) changing one item eliminates other information.

Second Normal Form

A relation is said to be in Second Normal Form when every nonkey attribute is fully functionally dependent on the primary key.

That is, every nonkey attribute needs the full primary key for unique identification

Second Normal Form

1NF Storage Anomalies Removed

Insertion: Can now enter new patients without surgery.

Insertion: Can now enter Surgeons who haven’t operated.

Deletion (type 1): If Charles Brown dies the corresponding tuples from Patient and Surgery tables can be deleted without losing information on David Rosen.

Update: If John White comes in for third time, and has moved, we only need to change the Patient table

2NF Storage Anomalies

Insertion: Cannot enter the fact that a particular drug has a particular side effect unless it is given to a patient.

Deletion: If John White receives some other drug because of the penicillin rash, and a new drug and side effect are entered, we lose the information that penicillin can cause a rash

Update: If drug side effects change (a new formula) we have to update multiple occurrences of side effects.

Third Normal Form

A relation is said to be in Third Normal Form if there is no transitive functional dependency between nonkey attributes

When one nonkey attribute can be determined with one or more nonkey attributes there is said to be a transitive functional dependency.

The side effect column in the Surgery table is determined by the drug administered

Side effect is transitively functionally dependent on drug so Surgery is not 3NF

Third Normal Form

2NF Storage Anomalies Removed

Insertion: We can now enter the fact that a particular drug has a particular side effect in the Drug relation.

Deletion: If John White recieves some other drug as a result of the rash from penicillin, but the information on penicillin and rash is maintained.

Update: The side effects for each drug appear only once.

Boyce-Codd Normal Form

Most 3NF relations are also BCNF relations.

A 3NF relation is NOT in BCNF if:

Candidate keys in the relation are composite keys (they are not single attributes)

There is more than one candidate key in the relation, and

The keys are not disjoint, that is, some attributes in the keys are common

Most 3NF Relations are also BCNF

Effectiveness and Efficiency Issues for DBMS

Focus on the relational model

Any column in a relational database can be searched for values.

To improve efficiency indexes using storage structures such as BTrees and Hashing are used

But many useful functions are not indexable and require complete scans of the the database

Example: Text Fields

In conventional RDBMS, when a text field is indexed, only exact matching of the text field contents (or Greater-than and Less-than).

Can search for individual words using pattern matching, but a full scan is required.

Text searching is still done best (and fastest) by specialized text search programs (Search Engines) that we will look at more later.

Normalizing to death

Normalization splits database information across multiple tables.

To retrieve complete information from a normalized database, the JOIN operation must be used.

JOIN tends to be expensive in terms of processing time, and very large joins are very expensive.

Advantages of RDBMS

Possible to design complex data storage and retrieval systems with ease (and without programming).

Support for ACID transactions

Atomic

Consistent

Independent

Durable

Advantages of RDBMS

Support for very large databases

Automatic optimization of searching (when possible)

RDBMS have a simple view of the database that conforms to much of the data used in businesses.

Standard query language (SQL)

Disadvantages of RDBMS

Until recently, no support for complex objects such as documents, video, images, spatial or time-series data. (ORDBMS are adding support these).

Often poor support for storage of complex objects. (Disassembling the car to park it in the garage)

Still no efficient and effective integrated support for things like text searching within fields.

Assignment

Examine the Cookie database using Access and look at the ER Diagram for it posted on the assignments page.

Consider the possibilities of Book publications

What are the problems with the database?

What new fields would you add to the database, and where?

Draw a new ER diagram showing your design.

Cookie ER diagram