2. What is a Data Model? DATA MODEL The specification of data structures and business rules to represent business requirements. student id student last name student first name student dormitory student major STUDENT course id course title course number of credits course location course instructor name COURSE attends/ is taught to
12. How do we determine keys? CANDIDATE KEY Any attribute or group of attributes which serves to uniquely identify each instance of an ENTITY. BOOK BOOK BOOK author first name author last name book title book edition book publisher book year published book isbn book lc catalog number author first name author last name book title book edition book publisher book year published book isbn book lc catalog number author first name author last name book title book edition book publisher book year published book isbn book lc catalog number
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14. Surrogate Keys transaction id account id customer id cash machine id transaction date CASH MACHINE TRANSACTION account id customer id cash machine id transaction date SURROGATE KEY A contrived, non-intelligent, single-attribute key used to replace a long composite key. Composite Key Surrogate Key CASH MACHINE TRANSACTION
15. Relationships MOVIE MOVIE COPY is rented as RELATIONSHIP A logical link between two entities that represents a business rule or constraint.
16. Foreign Keys FOREIGN KEY (FK) A primary key of a parent entity that is contributed to a child entity across a relationship. contains order number (FK) line item sequence number product code line item quantity line item number line item description LINE ITEM ORDER order number order date order sales representative order customer
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19. Relationship Cardinality PASSENGER AIRPLANE SEAT is ticketed for Z Each parent instance is related to zero, one, or more child instances Each parent instance is related to one or more child instances Each parent instance is related to zero or one child instances Each parent instance is related to exactly “N” child instances CUSTOMER ORDER places DRIVER INSURANCE POLICY covers P TIRE CAR requires N
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Notes de l'éditeur
Data models are the communications devices used for the representation of data, generally depicting the entities or “things” of interest to an organization and the relationships between those entities. Data models are an important part of the systems development process; they improve communications with users, and provide a sound logical basis for data base design. Data modeling is the process of creating these communications devices. It is a method of visualizing informational needs and typically takes the form of an ERD (Entity Relationship Diagram). Data modeling is the process used to analyze the data, identify the relationships among these data objects, and create the data model.
The Conceptual Data Model is a structured business view of the data required to support current business processes, business events, and related performance measurements. This is a single integrated data structure which reflects the structure of the business functions rather than processing flow or physical arrangement of data. It represents the overall logical structure of data required to support the business requirements independent of any software or data storage structure. A conceptual model often contains data objects not yet implemented in physical databases. It is a formal representation of the data needed to run an enterprise or a business activity.
The conceptual model can then be used to create the logical level, which maps to the designer view in the Zachman framework. The logical model would still be without reference to any specific DBMS, however it would include references to characteristics of databases that are generic in nature (i.e. indices, integrity constraints). It also adds more key and non-key attributes. A Conceptual Data Model represents the entities, which the owners feel are important for doing business. It gives a formal representation of the data needed to run an enterprise or a business activity. The conceptual data model is the owner’s view of the business, and will communicate the framework of the organization to the designers. Conceptual Data Models should be reviewed with business and technical users to ensure the following: to enforce common names, data types and size for the same data elements residing in the operational data store and the data warehouse to enforce common definitions of terms across environments and different business units to ensure agreement on the scope of the data requirements. The Conceptual Data Model (CDM), in conjunction with the business process model, will be used to design both OLTP (On-line Transactional Processing) systems and OLAP (On-line Analytical Processing) systems.
A Logical Data Model builds upon the business requirements and includes a further level of detail that supports both the business and system requirements. Like the Conceptual Data Model, the Logical Data Model is independent of specific software and data storage structures. Indexes and foreign keys are characteristics of databases that are generic in nature and required of the system for processing. Therefore, a Logical Data Model stores those characteristics without adding anything specific to a single DBMS. Once the development of the logical model is complete, this model can be used to create the physical data model, also known as the builder’s view. This model will reflect characteristics of databases that are the specific requirements of the data stores and the DBMS.