1. Chapter 2 Database System Concepts and Architecture

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.
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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.
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4. A data model is often specified by a database schema typically displayed in a schema diagram that consists of schema constructs.
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5. University Database Schema Diagram
fig 2.1
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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.
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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.
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8. External /High Level External External View1 View1 Conceptual Schema
Internal Schema
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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)
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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.
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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
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12. Parametric end users are provided with tailored interfaces for canned transactions that are designed by a systems analyst.
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13. Components of a DBMS
fig 2.3
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14. Database System Utilities
Loading
Conversion
Backup
File Reorganization
Performance monitoring
Communication
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15. Database Classifications
Single-user vs. Multiuser
Centralized vs. Distributed
Data Model
Relational
Network
Hierarchical
Object-oriented
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