Discussion of Normalization Algorithms and Alternative Relational Designs
16.4.2 Discussion of Normalization Algorithms and Alternative Relational Designs
One of the problems with the normalization algorithms we described is that the
566 Chapter 16 Relational Database Design Algorithms and Further Dependencies
the database attributes. This is not a simple task for a large database with hundreds of attributes. Failure to specify one or two important dependencies may result in an undesirable design. Another problem is that these algorithms are not deterministic in general. For example, the synthesis algorithms (Algorithms 16.4 and 16.6) require the specification of a minimal cover G for the set of functional dependencies F. Because there may be in general many minimal covers corresponding to F, as we illustrated in Example 2 of Algorithm 16.6 above, the algorithm can give different designs depending on the particular minimal cover used. Some of these designs may not be desirable. The decomposition algorithm to achieve BCNF (Algorithm 16.5) depends on the order in which the functional dependencies are supplied to the algo- rithm to check for BCNF violation. Again, it is possible that many different designs may arise corresponding to the same set of functional dependencies, depending on the order in which such dependencies are considered for violation of BCNF. Some of the designs may be preferred, whereas others may be undesirable.
It is not always possible to find a decomposition into relation schemas that pre- serves dependencies and allows each relation schema in the decomposition to be in BCNF (instead of 3NF as in Algorithm 16.6). We can check the 3NF relation schemas in the decomposition individually to see whether each satisfies BCNF. If some relation schema R i is not in BCNF, we can choose to decompose it further or to leave it as it is in 3NF (with some possible update anomalies).
To illustrate the above points, let us revisit the LOTS1A relation in Figure 15.13(a). It is a relation in 3NF, which is not in BCNF as was shown in Section 15.5. We also showed that starting with the functional dependencies (FD1, FD2, and FD5 in Figure 15.13(a)), using the bottom-up approach to design and applying Algorithm
16.6, it is possible to either come up with the LOTS1A relation as the 3NF design (which was called design X previously), or an alternate design Y which consists of three relations S 1 ,S 2 ,S 3 (design Y), each of which is a 3NF relation. Note that if we test design Y further for BCNF, each of S 1 ,S 2 , and S 3 turn out to be individually in BCNF. The design X, however, when tested for BCNF, fails the test. It yields the two relations S 1 and S 3 by applying Algorithm 16.5 (because of the violating functional dependency A → C ). Thus, the bottom-up design procedure of applying Algorithm
16.6 to design 3NF relations to achieve both properties and then applying Algorithm 16.5 to achieve BCNF with the nonadditive join property (and sacrific- ing functional dependency preservation) yields S 1 ,S 2 ,S 3 as the final BCNF design by one route (Y design route) and S 1 ,S 3 by the other route (X design route). This happens due to the multiple minimal covers for the original set of functional dependencies. Note that S 2 is a redundant relation in the Y design; however, it does not violate the nonadditive join constraint. It is easy to see that S 2 is a valid and meaningful relation that has the two candidate keys ( L , C ), and P placed side-by- side.
Table 16.1 summarizes the properties of the algorithms discussed in this chapter so far.
16.5 Futher Discussion of Multivalued Dependencies and 4NF 567
Table 16.1 Summary of the Algorithms Discussed in This Chapter Algorithm Input
Output
Properties/Purpose
Remarks
16.1 An attribute or a set
The closure of a key of attributes X, and a the closure of X with attributes that can be is the entire relation set of FDs F
A set of attrbutes in Determine all the
respect to F
functionally deter- mined from X
Multiple minimal dependencies F
16.2 A set of functional
The minimal cover
To determine the
of functional
minimal cover of a
covers may exist—
dependencies
set of dependencies F depends on the order of selecting function- al dependencies
16.2a Relation schema R
The entire relation R with a set of func-
Key K of R
To find a key K
(that is a subset of R) is always a default tional dependencies
superkey
16.3 A decomposition D Boolean result: yes or Testing for nonaddi- See a simpler test of R and a set F of
tive join decomposi- NJB in Section 16.2.4 functional depen-
no for nonadditive
for binary decompo- dencies
join property
tion
sitions
A set of relations in Dependency preser- No guarantee of sat- set of functional
16.4 A relation R and a
isfying lossless join dependencies F
No guarantee of set of functional
16.5 A relation R and a
A set of relations in Nonadditive join
dependency preser- dependencies F
May not achieve set of functional
16.6 A relation R and a
A set of relations in Nonadditive join
BCNF, but achieves dependencies F
3NF
and dependency-
preserving decompo- all desirable proper- sition
ties and 3NF
No guarantee of set of functional and 4NF
16.7 A relation R and a
A set of relations in Nonadditive join
dependency preser- multivalued depen-
decomposition
vation dencies
Parts
» Fundamentals_of_Database_Systems,_6th_Edition
» Characteristics of the Database Approach
» Advantages of Using the DBMS Approach
» A Brief History of Database Applications
» Schemas, Instances, and Database State
» The Three-Schema Architecture
» The Database System Environment
» Centralized and Client/Server Architectures for DBMSs
» Classification of Database Management Systems
» Domains, Attributes, Tuples, and Relations
» Key Constraints and Constraints on NULL Values
» Relational Databases and Relational Database Schemas
» Integrity, Referential Integrity, and Foreign Keys
» Update Operations, Transactions, and Dealing with Constraint Violations
» SQL Data Definition and Data Types
» Specifying Constraints in SQL
» The SELECT-FROM-WHERE Structure of Basic SQL Queries
» Ambiguous Attribute Names, Aliasing, Renaming, and Tuple Variables
» Substring Pattern Matching and Arithmetic Operators
» INSERT, DELETE, and UPDATE Statements in SQL
» Comparisons Involving NULL and Three-Valued Logic
» Nested Queries, Tuples, and Set/Multiset Comparisons
» The EXISTS and UNIQUE Functions in SQL
» Joined Tables in SQL and Outer Joins
» Grouping: The GROUP BY and HAVING Clauses
» Discussion and Summary of SQL Queries
» Specifying General Constraints as Assertions in SQL
» Introduction to Triggers in SQL
» Specification of Views in SQL
» View Implementation, View Update, and Inline Views
» Schema Change Statements in SQL
» Sequences of Operations and the RENAME Operation
» The UNION, INTERSECTION, and MINUS Operations
» The CARTESIAN PRODUCT (CROSS PRODUCT) Operation
» Variations of JOIN: The EQUIJOIN and NATURAL JOIN
» Additional Relational Operations
» Examples of Queries in Relational Algebra
» The Tuple Relational Calculus
» The Domain Relational Calculus
» Using High-Level Conceptual Data Models
» Entity Types, Entity Sets, Keys, and Value Sets
» Relationship Types, Relationship Sets, Roles, and Structural Constraints
» ER Diagrams, Naming Conventions, and Design Issues
» Example of Other Notation: UML Class Diagrams
» Relationship Types of Degree Higher than Two
» Subclasses, Superclasses, and Inheritance
» Constraints on Specialization and Generalization
» Specialization and Generalization Hierarchies
» Modeling of UNION Types Using Categories
» A Sample UNIVERSITY EER Schema, Design Choices, and Formal Definitions
» Data Abstraction, Knowledge Representation, and Ontology Concepts
» ER-to-Relational Mapping Algorithm
» Discussion and Summary of Mapping for ER Model Constructs
» Mapping EER Model Constructs
» The Role of Information Systems
» The Database Design and Implementation Process
» Use of UML Diagrams as an Aid to Database Design Specification 6
» Rational Rose: A UML-Based Design Tool
» Automated Database Design Tools
» Introduction to Object-Oriented Concepts and Features
» Object Identity, and Objects versus Literals
» Complex Type Structures for Objects and Literals
» Encapsulation of Operations and Persistence of Objects
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» Overview of the Object Model of ODMG
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» Atomic (User-Defined) Objects
» Extents, Keys, and Factory Objects
» The Object Definition Language ODL
» Differences between Conceptual Design of ODB and RDB
» Mapping an EER Schema to an ODB Schema
» Query Results and Path Expressions
» Overview of the C++ Language Binding in the ODMG Standard
» Structured, Semistructured, and Unstructured Data
» XML Hierarchical (Tree) Data Model
» Well-Formed and Valid XML Documents and XML DTD
» XPath: Specifying Path Expressions in XML
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» Extracting XML Documents from
» Database Programming: Techniques
» Retrieving Single Tuples with Embedded SQL
» Retrieving Multiple Tuples with Embedded SQL Using Cursors
» Specifying Queries at Runtime Using Dynamic SQL
» SQLJ: Embedding SQL Commands in Java
» Retrieving Multiple Tuples in SQLJ Using Iterators
» Database Programming with SQL/CLI Using C
» JDBC: SQL Function Calls for Java Programming
» Database Stored Procedures and SQL/PSM
» PHP Variables, Data Types, and Programming Constructs
» Overview of PHP Database Programming
» Imparting Clear Semantics to Attributes in Relations
» Redundant Information in Tuples and Update Anomalies
» Normal Forms Based on Primary Keys
» General Definitions of Second and Third Normal Forms
» Multivalued Dependency and Fourth Normal Form
» Join Dependencies and Fifth Normal Form
» Inference Rules for Functional Dependencies
» Minimal Sets of Functional Dependencies
» Properties of Relational Decompositions
» Dependency-Preserving Decomposition
» Dependency-Preserving and Nonadditive (Lossless) Join Decomposition into 3NF Schemas
» Problems with NULL Values and Dangling Tuples
» Discussion of Normalization Algorithms and Alternative Relational Designs
» Further Discussion of Multivalued Dependencies and 4NF
» Other Dependencies and Normal Forms
» Memory Hierarchies and Storage Devices
» Hardware Description of Disk Devices
» Magnetic Tape Storage Devices
» Placing File Records on Disk
» Files of Unordered Records (Heap Files)
» Files of Ordered Records (Sorted Files)
» External Hashing for Disk Files
» Hashing Techniques That Allow Dynamic File Expansion
» Other Primary File Organizations
» Parallelizing Disk Access Using RAID Technology
» Types of Single-Level Ordered Indexes
» Some General Issues Concerning Indexing
» Algorithms for External Sorting
» Implementing the SELECT Operation
» Implementing the JOIN Operation
» Algorithms for PROJECT and Set
» Notation for Query Trees and Query Graphs
» Heuristic Optimization of Query Trees
» Catalog Information Used in Cost Functions
» Examples of Cost Functions for SELECT
» Examples of Cost Functions for JOIN
» Example to Illustrate Cost-Based Query Optimization
» Factors That Influence Physical Database Design
» Physical Database Design Decisions
» An Overview of Database Tuning in Relational Systems
» Transactions, Database Items, Read and Write Operations, and DBMS Buffers
» Why Concurrency Control Is Needed
» Transaction and System Concepts
» Desirable Properties of Transactions
» Serial, Nonserial, and Conflict-Serializable Schedules
» Testing for Conflict Serializability of a Schedule
» How Serializability Is Used for Concurrency Control
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» Dealing with Deadlock and Starvation
» Concurrency Control Based on Timestamp Ordering
» Multiversion Concurrency Control Techniques
» Validation (Optimistic) Concurrency
» Granularity of Data Items and Multiple Granularity Locking
» Using Locks for Concurrency Control in Indexes
» Other Concurrency Control Issues
» Recovery Outline and Categorization of Recovery Algorithms
» Caching (Buffering) of Disk Blocks
» Write-Ahead Logging, Steal/No-Steal, and Force/No-Force
» Transaction Rollback and Cascading Rollback
» NO-UNDO/REDO Recovery Based on Deferred Update
» Recovery Techniques Based on Immediate Update
» The ARIES Recovery Algorithm
» Recovery in Multidatabase Systems
» Introduction to Database Security Issues 1
» Discretionary Access Control Based on Granting and Revoking Privileges
» Mandatory Access Control and Role-Based Access Control for Multilevel Security
» Introduction to Statistical Database Security
» Introduction to Flow Control
» Encryption and Public Key Infrastructures
» Challenges of Database Security
» Distributed Database Concepts 1
» Types of Distributed Database Systems
» Distributed Database Architectures
» Data Replication and Allocation
» Example of Fragmentation, Allocation, and Replication
» Query Processing and Optimization in Distributed Databases
» Overview of Transaction Management in Distributed Databases
» Overview of Concurrency Control and Recovery in Distributed Databases
» Current Trends in Distributed Databases
» Distributed Databases in Oracle 13
» Generalized Model for Active Databases and Oracle Triggers
» Design and Implementation Issues for Active Databases
» Examples of Statement-Level Active Rules
» Time Representation, Calendars, and Time Dimensions
» Incorporating Time in Relational Databases Using Tuple Versioning
» Incorporating Time in Object-Oriented Databases Using Attribute Versioning
» Temporal Querying Constructs and the TSQL2 Language
» Spatial Database Concepts 24
» Multimedia Database Concepts
» Clausal Form and Horn Clauses
» Datalog Programs and Their Safety
» Evaluation of Nonrecursive Datalog Queries
» Introduction to Information Retrieval
» Types of Queries in IR Systems
» Evaluation Measures of Search Relevance
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» Analyzing the Link Structure of Web Pages
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» Market-Basket Model, Support, and Confidence
» Frequent-Pattern (FP) Tree and FP-Growth Algorithm
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» Grouping, Aggregation, and Database Modification in QBE
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