Part4 Methodology of Database Design Chapter 07- Overview of Conceptual Database Design Lu Wei College of Software and Microelectronics Northwestern Polytechnical University Database Systems

Lu Wei2 Outline What is a Design Methodology Conceptual, Logical, and Physical Database Design Overview of the Database Design Methodology Conceptual Database Design Methodology

Lu Wei3 Outline What is a Design Methodology Conceptual, Logical, and Physical Database Design Overview of the Database Design Methodology Conceptual Database Design Methodology

Lu Wei4 What is a Design Methodology Design Methodology –A structured approach that uses procedures, techniques, tools, and documentation aids to support and facilitate the process of design.

Lu Wei5 Outline What is a Design Methodology Conceptual, Logical, and Physical Database Design Overview of the Database Design Methodology Conceptual Database Design Methodology

Lu Wei6 Conceptual, Logical, and Physical Database Design In presenting this database design methodology, the design process is divided into three main phases: conceptual, logical, and physical database design.

Lu Wei7 Conceptual, Logical, and Physical Database Design Conceptual database design –The process of constructing a model of the information used in an enterprise, independent of all physical considerations.

Lu Wei8 Conceptual, Logical, and Physical Database Design Logical database design –The process of constructing a model of the information used in an enterprise based on a specific data model, but independent of a particular DBMS and other physical considerations. The logical database design phase maps the conceptual model on to a logical model, which is influenced by the data model for the target database.

Lu Wei9 Conceptual, Logical, and Physical Database Design Physical database design –The process of producing a description of the implementation of the database on secondary storage; it describes the base relations, file organizations, and indexes used to achieve efficient access to the data, and any associated integrity constraints and security measures. There is feedback between physical and logical design, because decisions taken during physical design for improving performance may affect the logical data model.

Lu Wei10 Outline What is a Design Methodology Conceptual, Logical, and Physical Database Design Overview of the Database Design Methodology Conceptual Database Design Methodology

Lu Wei11 Overview of the Database Design Methodology Conceptual database design –Step 1 Build local conceptual data model for each view Step 1.1 Identify entity types Step 1.2 Identify relationship types Step 1.3 Identify and associate attributes with entity or relationship types Step 1.4 Determine attribute domains Step 1.5 Determine candidate and primary key attributes Step 1.6 Consider use of enhanced modeling concepts (optional step) Step 1.7 Check model for redundancy Step 1.8 Validate local conceptual model against user transactions Step 1.9 Review local conceptual data model with user

Lu Wei12 Overview of the Database Design Methodology Logical database design for the relation model –Step 2 Build and validate local logical data model for each view Step 2.1 Remove features not compatible with the relational model (optional step) Step 2.2 Derive relations for local logical data model Step 2.3 Validate relations using normalization Step 2.4 Validate relations against user transactions Step 2.5 Define integrity constraints Step 2.6 Review local logical data model with user

Lu Wei13 Overview of the Database Design Methodology Logical database design for the relation model –Step 3 Build and validate global logical data model Step 3.1 Merge local logical data models into global model Step 3.2 Validate global logical data model Step 3.3 Check for future growth Step 3.4 Review global logical data model with users

Lu Wei14 Overview of the Database Design Methodology Physical database design for relational database –Step 4 Translate global logical data model for target DBMS Step 4.1 Design base relations Step 4.2 Design representation of derived data Step 4.3 Design enterprise constraints

Lu Wei15 Overview of the Database Design Methodology Physical database design for relational database –Step 5 Design physical representation Step 5.1 Analyze transactions Step 5.2 Choose file organizations Step 5.3 Choose indexes Step 5.4 Estimate disk space requirements

Lu Wei16 Overview of the Database Design Methodology Physical database design for relational database –Step 6 Design user views –Step 7 Design security mechanisms –Step 8 Consider the introduction of controlled redundancy –Step 9 Monitor and tune the operational system

Lu Wei17 Overview of the Database Design Methodology Throughout this methodology, users play a critical role in continually reviewing and validating the data model and the supporting documentation. Database design is an iterative process, which has a starting point and an almost endless procession of refinements. The methodology should act as a framework to help guide the designer through database design effectively.

Lu Wei18 Outline What is a Design Methodology Conceptual, Logical, and Physical Database Design Overview of the Database Design Methodology Conceptual Database Design Methodology

Lu Wei19 Conceptual Database Design Methodology Step 1 Build Local Conceptual Data Model for Each View –Objective: To build a local conceptual data model of an enterprise for each specific view. –Each local conceptual data model comprises: Entity types Relationship types Attributes and attribute domains Primary keys and alternate keys Integrity constraints.

Lu Wei20 Conceptual Database Design Methodology Step 1 Build Local Conceptual Data Model for Each View –The results of step 1 comprises: An ER diagram Supporting documentation

Lu Wei21 Conceptual Database Design Methodology Step 1.1 Identify entity types –approaches to identify entities Examine the user’s requirements specification to identify nouns or noun phrases mentioned. Look for objects that have an existence in their own right. –It is not always obvious whether a particular object is an entity, a relationship, or an attribute. For example, how would we classify marriage? –Design is subjective and different designers may produce different, but equally valid, interpretations.

Lu Wei22 Conceptual Database Design Methodology Step 1.1 Identify entity types –The activity therefore relies, to a certain extent, on judgement and experience. –There may be no unique set of entity deducible from a given requirements specification. But all the result deducibled should be at least adequate for the system required. –Results in this step Documentation of entity types (entity name, description, aliases, occurrence)

Lu Wei23 Conceptual Database Design Methodology Step 1.2 Identify relationship types –approaches to identify relationships Examine the user’s requirements specification to identify verbs or verbal expressions mentioned. Some relationships are explicit but some are implicit. –In most instances, the relationships are binary. However, we should be careful to look out for complex relationships that may involve more than two entity types and recursive relationships that involve only one entity type.

Lu Wei24 Conceptual Database Design Methodology Step 1.2 Identify relationship types –Determine the multiplicity constraints of relationship types A model that includes multiplicity constraints more explicitly represents the semantics of the relationships and results in a better representation of the enterprise. –Check that each entity participates in at least one relationship –Use ER diagrams

Lu Wei25 Conceptual Database Design Methodology Step 1.2 Identify relationship types –Results in this step ER model diagrams Documentation of relationship types

Lu Wei26 Conceptual Database Design Methodology 1.3 Identify and associate attributes with entity or relationship types –Attribute types comprise: Simple/composite attributes Single/multi-valued attributes Derived attributes –We should ensure that an attribute is associated with only one entity or relationship type. –Results in this step Documentation of attributes

Lu Wei27 Conceptual Database Design Methodology 1.4 determine attribute domains –Results in this step Documentation of attribute domains Update the data dictionary entries for attributes to record their domain in place of the data type and length information

Lu Wei28 Conceptual Database Design Methodology 1.5 determine candidate and primary key attributes –Guidelines to help choose a primary key from the candidate keys. Choose the candidate key with the minimal set of attributes that is lease likely to have its values changed with fewest characters (for textual attributes) with smallest maximum value (for numerical attributes) That is easiest to use from the users’ point of view –Results in this step Documentation of primary and alternate keys

Lu Wei29 Conceptual Database Design Methodology 1.6 Consider use of enhanced modeling concepts (optional step)

Lu Wei30 Conceptual Database Design Methodology 1.7 Check model for redundancy

Lu Wei31 Conceptual Database Design Methodology 1.8 Validate local conceptual model against user transactions –The objective of this step is to check the model to ensure that the model supports the transactions required by this view. –approaches to check the model Describing the transactions Using transaction pathways –

Lu Wei32 Conceptual Database Design Methodology 1.9 Review local conceptual data model with user

Lu Wei33 Summary