Module-02-Advanced-Data-Modeling.pdf_20240929_142834_0000.pdf

Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 STUDY GUIDE FOR MODULE 02...

Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 STUDY GUIDE FOR MODULE 02 ADVANCED DATA MODELING OBJECTIVES At the end of this module, students are expected to:  Identify the main characteristics of entity relationship component.  Describe the process of database design.  Identify the Extended Entity Relationship (EER) model and describe how this concept becomes a good foundation for a successful application development. CONTENTS Extended Entity Relationship Model - Result of adding more semantic constructs to original entity relationship (ER) model - Diagram using this model is called an EER diagram (EERD) Entity Supertypes and Subtypes Entity Supertype - Generic entity type related to one or more entity subtypes - Contains common characteristics Entity subtype - Contains unique characteristics of each entity subtype PANGASINAN STATE UNIVERSITY 1 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Specialization Hierarchy - Depicts arrangement of higher-level entity supertypes and lower-level entity subtypes - Relationships described in terms of “IS-A” relationships - Subtype exists only within context of Supertype - Every subtype has only one supertype to which it is directly related - Can have many levels of supertype/subtype relationships Inheritance - Enables entity subtype to inherit attributes and relationships of supertype - All entity subtypes inherit their primary key attribute from their supertype - At implementation level, supertype and its subtype(s) maintain a 1:1 relationship - Entity subtypes inherit all relationships in which supertype entity participates - Lower-level subtypes inherit all attributes and relationships from all upper-level supertypes PANGASINAN STATE UNIVERSITY 2 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Subtype Discriminator - Attribute in supertype entity - Determines to which entity subtype each supertype occurrence is related - Default comparison condition for subtype discriminator attribute is equality comparison - Subtype discriminator may be based on other comparison condition Disjoint and Overlapping Constraints - Disjoint subtypes - Also called nonoverlapping subtypes - Subtypes that contain unique subset of supertype entity set - - Overlapping subtypes Subtypes that contain nonunique subsets of supertype entity set PANGASINAN STATE UNIVERSITY 3 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Completeness Constraints - Specifies whether entity supertype occurrence must be a member of at least one subtype - Partial completeness - Symbolized by a circle over a single line - Some supertype occurrences are not members of any subtype - Total completeness - Symbolized by a circle over a double line - Every supertype occurrence must be member of at least one subtype Specialization and Generalization Specialization - Identifies more specific entity subtypes from higher-level entity supertype - Top-down process - Based on grouping unique characteristics and relationships of the subtypes Generalization - Identifies more generic entity supertype from lower-level entity subtypes - Bottom-up process - Based on grouping common characteristics and relationships of the subtypes Entity Clustering - “Virtual” entity type used to represent multiple entities and relationships in ERD - Considered “virtual” or “abstract” because it is not actually an entity in final ERD - Temporary entity used to represent multiple entities and relationships - Eliminate undesirable consequences - Avoid display of attributes when entity clusters are used PANGASINAN STATE UNIVERSITY 4 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Entity Integrity: Selecting Primary Keys - Primary key is the most important characteristic of an entity -Single attribute or some combination of attributes - Primary key’s function is to guarantee entity integrity - Primary keys and foreign keys work together to implement relationships - Properly selecting primary key has direct bearing on efficiency and effectiveness Natural Keys and Primary Keys - Natural key is a real-world identifier used to uniquely identify real-world objects - Familiar to end users and forms part of their day-to-day business vocabulary - Generally, data modeler uses natural identifier as primary key of entity being modeled - May instead use composite primary key or surrogate key PANGASINAN STATE UNIVERSITY 5 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Primary Key Guidelines - Attribute that uniquely identifies entity instances in an entity set - Could also be combination of attributes - Main function is to uniquely identify an entity instance or row within a table - Guarantee entity integrity, not to “describe” the entity - Primary keys and foreign keys implement relationships among entities - Behind the scenes, hidden from user When to Use Composite Primary Keys - Composite primary keys useful in two cases: - As identifiers of composite entities - In which each primary key combination is allowed once in M:N relationship - As identifiers of weak entities - In which weak entity has a strong identifying relationship with the parent entity Automatically provides benefit of ensuring that there cannot be duplicate values PANGASINAN STATE UNIVERSITY 6 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 When used as identifiers of weak entities normally used to represent: - Real-world object that is existent-dependent on another real-world object - Real-world object that is represented in data model as two separate entities in strong identifying relationship Dependent entity exists only when it is related to parent entity. When To Use Surrogate Primary Keys? - Especially helpful when there is: - No natural key - Selected candidate key has embedded semantic contents - Selected candidate key is too long or cumbersome If you use surrogate key: - Ensure that candidate key of entity in question performs properly - Use “unique index” and “not null” constraints PANGASINAN STATE UNIVERSITY 7 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Design Cases: Learning Flexible Database Design - Data modeling and design requires skills acquired through experience - Experience acquired through practice - Four special design cases that highlight: - Importance of flexible design - Proper identification of primary keys - Placement of foreign keys Design Case 1: Implementing 1:1 Relationships - Foreign keys work with primary keys to properly implement relationships in relational model - Put primary key of the “one” side on the “many” side as foreign key - Primary key: parent entity - Foreign key: dependent entity - In 1:1 relationship, there are two options: - Place a foreign key in both entities (not recommended) - Place a foreign key in one of the entities - Primary key of one of the two entities appears as foreign key of other PANGASINAN STATE UNIVERSITY 8 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Design Case 2: Maintaining History of Time-Variant Data - Normally, existing attribute values are replaced with new value without regard to previous value - Time-variant data: - Values change over time - Must keep a history of data changes -- Keeping history of time-variant data equivalent to having a multivalued attribute in your entity - Must create new entity in 1:M relationships with original entity New entity contains new value, date of change PANGASINAN STATE UNIVERSITY 9 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Design Case 3: Fan Traps - Design trap occurs when relationship is improperly or incompletely identified - Represented in a way not consistent with the real world - Most common design trap is known as fan trap - Fan trap occurs when one entity is in two 1:M relationships to other entities - Produces an association among other entities not expressed in the model PANGASINAN STATE UNIVERSITY 10 Prepared by: Edilberto L. Caralos Jr. FM-AA-C IA-15 Rev. 0 30-March-2021 Study Guide in IM 102 Information Management 2 Module No.2 Design Case 4: Redundant Relationships - Redundancy is seldom a good thing in database environment - Occurs when there are multiple relationship paths between related entities - Main concern is that redundant relationships remain consistent across model - Some designs use redundant relationships to simplify the design PANGASINAN STATE UNIVERSITY 11