Detailed Data Modeling

Outline Data Modeling Modeling Constructs –Entities –Relationships –Cardinality Model Basic Rules Advanced Rules Prototyping Process Modeling Homework

Data Modeling Why model data? –Data needs are relatively constant over time, as is the nature of data needed in a particular enterprise –Data is necessary for present and future decision making –Strategies for collecting data into a system have changed radically 1850 all manual, face to face, post (mail) 1900 still manual, telephone 1950 early computer applications and storage 2000 little manual, web-interface, enterprise systems –Data is static

Modeling Constructs Entity Relationship Attribute –Primary Key –Foreign Key –Simple –Composite –Derivable Cardinality –Broad business rules of min/max association Abstraction –Grouping by type, generalization, class (IS-A), super and subtypes

Entity Types –Persons - AGENT –Places - Locations –Objects - RESOURCES –Events - EVENTS –Concepts – Artifacts Instance –Single occurrence of any specific Entity

Attribute Broad Characteristics Classification for each specific entity type Descriptive property –Element, property, field –Compound attributes Domain – restricted values – validation rules, look-up tables Identification –Single value key –Compound key –Concatenated key

Relationship Natural organizational association –Registered in; Purchase of; Sale of; Receipt of; Payment for; Typically related to an event –Assigned to a department; Declared major; –Detail of natural organizational association Items purchased; Time worked; Repairs made;

Cardinality Minimum/maximum associations between entities –Agent sells/buys many products –Employee works on many projects –Employee works in ONE department Mandatory –At least one instance per each association must exist Parent (Mandatory dual relationship based on …) Optional –An instance per association may not exist Marriage Different representations –Crowsfoot, Chen, others

Types of Relationships Recursive –Exists with same entity type Ex: Bill of Materials (inventory/products); Marriage (People) Non-Identifying –Entity exists on its own Identifying –Entity exists because of another entity (also called ‘Dependent’, ‘Attributive’ One to Many Many to Many

Associative Entity Entity with a base in an association Inherits primary (Compound) key from more than one entity –Purchase/Sales order detail (Order#, Item #) –Shipping detail (Shipping Doc#, Item #) –Time Card detail (esp. projects/jobs) (Time Card#, Project/Job #) Second Normal Form

Generalization Also known as IS A relationship, CLASS –Supertype Attributes used by other entity (subtype) –People –Subtype Inherits attributes from supertype Has additional set of attributes –Student, Employee May or may not be multiple subtypes –Student, Employee, Alumni (inclusive) –Salaried, hourly (exclusive)

Conceptual Modeling Summary Entity Relationship Model –Chen, 1976 Entity –Noun, Attributes Relationship –Verb, Cardinality –Natural business association –Duality Set Theory Notation –See Table 4-1; Figure 8-3 (Whitten, 316/299) REA Model CASE Tool (Visible Analyst) Visio

Normalization Strategy used in evolving data model First Normal Form (1NF) –Remove repeating groups – no more than one value for a single instance of that entity Second Normal Form (2NF) –All non-key attributes dependent upon full primary key (Compound Key) and in 1NF Third Normal Form (3NF) –All non-key attributes not dependent on another non-key attribute and in 2NF REMEMBER – All values to be dependent upon the primary key, and ONLY the primary key

ERD and REA REA derived from ERD REA reflects duality of event, critical for enterprise modeling REA supplements ERD –Add duality Accounts as artifacts –Organizational rules –Queries

ERD to Data Design (Access) Entities correspond to tables in RDBMS; Stores in Data Flow Diagram Convert ERD to Relational Model (Design Phase), Tables for Physical Design Access - Associate (in Relationship screen) Primary Key Attribute (field) of ONE side to Foreign Key Attribute (field) of MANY side –Enforce Referential Integrity Rules, if desired

Homework Chapter 9 Problems and Exercises –1 –6 –7 –17