1. Chapter 2Database System ConceptsandArchitecture Chapter 2

2. Data Models • A data model is a description of the structure of a database. Data models generally, fall into 3 categories according to the level of the description. Chapter 2

3. High-level ( or conceptual) data models closely approximate the miniworld. • Representational ( or, implementational ) data models are intermediate data models close to the miniworld but also reflecting the actual organization of data in the database. • Low-level ( or, physical) data models describe details of physical storage, generally transparent to casual or parametric end users. Chapter 2

4. A data model is often specified by a database schema typically displayed in a schema diagram that consists of schema constructs. Chapter 2

5. University Database SchemaDiagram • fig 2.1 Chapter 2

6. Database State • The actual data in a data base at a particular instant is the database state, which consists of a set of instances for each schema construct. • Defining a database consists of specifying a schema to the DBMS. We then have a database in an empty state, with no data. Chapter 2

7. When data is first loaded, the database is in its initial state. • Subsequently, each update creates another state. The DBMS must guarantee that each such state is a valid state that satisfies schema specifications. • The schema is the intension, while a database state is the extension of the schema. Chapter 2

8. Conceptual Schema Internal Schema External /High Level External View1 External View1 Chapter 2

9. DBMS Languages • DDL - Data Definition Language is used to define both schemas. • VDL - View Definition Language is used to specify the mapping of the user views to the conceptual schema. • DML - Data Manipulation Language is used to provide a means to manipulate the database. (I.e. insert, delete, query,etc) Chapter 2

10. Most DBMS’s combine the various capabilities of the DDL, VDL, DML and SDL into a single high-level DML (e.g. SQL relational database language.) • Such DML’s can generally be entered interactively from the terminal or embedded in a high-level language such as C which acts as a host language. Chapter 2

11. Common Approaches by Users • Typically, sophisticated end users embed the DML . • Casual end users usually access interactively through user-friendly interfaces created by too developers • Menu based interfaces • Graphical interfaces • Forms base interfaces Chapter 2

12. Parametric end users are provided with tailored interfaces for canned transactions that are designed by a systems analyst. Chapter 2

13. Components of a DBMS • fig 2.3 Chapter 2

14. Database System Utilities • Loading • Conversion • Backup • File Reorganization • Performance monitoring • Communication Chapter 2

15. Database Classifications • Single-user vs. Multiuser • Centralized vs. Distributed • Data Model • Relational • Network • Hierarchical • Object-oriented Chapter 2