Chapter 16 Methodology Conceptual Database Design 1 Design

Chapter 16 Methodology Conceptual Database Design 1

Design Methodology u Structured approach that uses procedures, techniques, tools, and documentation aids to support and facilitate the process of design u Three main phases – Conceptual database design – Logical database design – Physical database design 2

Database Design u u u Conceptual database design – Process of constructing model of data used in an enterprise, independent of all physical considerations Logical database design – Process of constructing model of data used in an enterprise based on specific data model (e. g. relational), independent of particular DBMS and other physical considerations Physical database design – Process of producing description of implementation of database on secondary storage » Describes base relations, file organizations, and indexes » Design used to achieve efficient access to data, and any associated integrity constraints and security measures 3

Critical Success Factors in Database Design u Work interactively with users as much as possible u Follow structured methodology throughout data modeling process u Employ data-driven approach u Incorporate structural and integrity considerations into data models u Combine conceptualization, normalization, and transaction validation techniques into data modeling methodology 4

Critical Success Factors in Database Design u Use diagrams to represent as much of data models as possible u Use Database Design Language (DBDL) to represent additional data semantics u Build data dictionary to supplement data model diagrams u Be willing to repeat steps 5

Overview Database Design Methodology Conceptual database design u Step 1 Build conceptual data model – 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, primary, and alternate key attributes 6

Overview Database Design Methodology u Step 1 Build conceptual data model (continue) – Step 1. 6 Consider use of enhanced modeling concepts (optional step) – Step 1. 7 Check model for redundancy – Step 1. 8 Validate conceptual model against user transactions – Step 1. 9 Review conceptual data model with user 7

Overview Database Design Methodology Logical database design for the relational model u Step 2 Build and validate logical data model – Step 2. 1 Derive relations for logical data model – Step 2. 2 Validate relations using normalization – Step 2. 3 Validate relations against user transactions – Step 2. 4 Define integrity constraints 8

Overview Database Design Methodology u Step 2 Build and validate logical data model (continue) – Step 2. 5 Review logical data model with user – Step 2. 6 Merge logical data models into global model (optional step) – Step 2. 7 Check for future growth 9

Overview Database Design Methodology Physical database design for relational database u Step 3 Translate logical data model for target DBMS – Step 3. 1 Design base relations – Step 3. 2 Design representation of derived data – Step 3. 3 Design general constraints 10

Overview Database Design Methodology u Step 4 Design file organizations and indexes – Step 4. 1 Analyze transactions – Step 4. 2 Choose file organization – Step 4. 3 Choose indexes – Step 4. 4 Estimate disk space requirements 11

Overview Database Design Methodology u Step 5 Design user views u Step 6 Design security mechanisms u Step 7 Consider the introduction of controlled redundancy u Step 8 Monitor and tune the operational system 12

Step 1 Build Conceptual Data u To build a conceptual data model of data requirements of enterprise – Model comprises entity types, relationship types, attributes and attribute domains, primary and alternate keys, and integrity constraints u Step 1. 1 Identify entity types – To identify required entity types – Typically nouns, noun phrases, major objects 13

Extract from data dictionary for Staff user views of Dream. Home showing description of entities 14

Step 1 Build Conceptual Data u Step 1. 2 Identify relationship types – To identify important relationships that exist between entity types – Typically verbs, verb phrases – Determine multiplicity constraints – Check for fan and chasm traps » Fan trap – 2 or more 1. . * fan out from same entity » Chasm trap – 1 or more 0. . * form part of pathway between related entities 15

Extract from data dictionary for Staff user views of Dream. Home showing description of relationships 16

First-cut ER diagram for Staff user views of Dream. Home 17

Step 1 Build Conceptual Data u Step 1. 3 Identify and associate attributes with entity or relationship types – To associate attributes with appropriate entity or relationship types and document details of each attribute – Determine information required u Step 1. 4 Determine attribute domains – To determine domains for attributes in data model and document details of each domain 18

Extract from data dictionary for Staff user views of Dream. Home showing description of attributes 19

Step 1 Build Conceptual Data u Step 1. 5 Determine candidate, primary, and alternate key attributes – To identify candidate key(s) for each entity and if there is more than one candidate key, to choose one to be primary key and others as alternate keys – Strong entity » Primary key easily identifiable – Weak entity » Primary key not identifiable » Need to map entity & relationship to owner entity to identify primary key 20

ER diagram for Staff user views of Dream. Home with primary keys added 21

Step 1 Build Conceptual Data u Step 1. 6 Consider use of enhanced modeling concepts (optional step) – To consider use of enhanced modeling concepts, such as specialization / generalization, aggregation, and composition 22

Revised ER diagram for Staff user views of Dream. Home with specialization / generalization 23

Step 1 Build Conceptual Data Model u Step 1. 7 Check model for redundancy – To check for presence of any redundancy in model and to remove any that does exist » Re-examine 1 -1 relationships » Remove redundant relationships – same information obtained via other relationships » Consider time dimension 24

Example of removing a redundant relationship called Rents 25

Example of a non-redundant relationship Father. Of (Time dimension example) 26

Step 1 Build Conceptual Data Model u Step 1. 8 Validate conceptual model against user transactions – To ensure that conceptual model supports required transactions » Describe transactions » Use transaction pathways u Example – List the details of properties managed by a named member of staff at the branch 27

Using pathways to check that the conceptual model supports the user transactions 28

Step 1 Build Conceptual Data Model u Step 1. 9 Review conceptual data model with user – To review conceptual data model with user to ensure that model is ‘true’ representation of data requirements of enterprise 29

User Specifications u Ph. D. students are required to keep a bibliography of all the things they read pertaining to their research. You need to design a database that will serve as their bibliography. They read journal articles, conference papers, books, book chapters, etc. They must be able to make notes about the item that has been read and they should be able to search based upon keywords. Each item has keywords. Finally, they should be able to store a reference for each item that has been read. Here is a sample reference: Gilbert, J. E. & Zhong, Y. (2003). Speech User Interfaces for Information Retrieval. In Proceedings of 12 th Annual ACM Conference on Information & Knowledge Management, New Orleans, Louisiana, pp. 77 -82. Here are some sample questions that the database should be able to answer: 1. When did I read a certain book chapter? 2. Show me all of my items that are Educational Technology articles. 3. Find an item titled “What should we teach our pants? ” 4. Who are the authors of an item? 5. Show me all the references recorded yesterday 30