Chapter-2- Database System Concepts and Architecture Text Book : “Fundamentals of Database Systems” Additional References: Prof. Beat Signer Lecture notes Dr.Lilac Safadi Lecture notes

DBMS Architectures There is a wide variety of different DBMS architectures File-Server Architecture Two-Tier Client-Server Architecture Three-Tier Client Server Architecture N-Tier Architecture Teleprocessing Peer-to-Peer Architecture Distributed DBMS Service-Oriented Architecture Cloud Architecture...

File-Server Architecture... A file-server is a computer that is connected to a network and mainly serves as a shared storage e.g. for realizing shared access to a database In a file-server architecture the processing is distributed over the network workstations (application and DBMS) request data (files)

Two-Tier Client-Server Architecture Application consists of a client (first tier) and a server (second tier) that might run on different machines clear separation of concerns between client and server thin client vs. thick client less or more application logic on the client side Supports decentralized business environments

Data Models, Schemas, and Instances Data abstraction Suppression of details of data organization and storage Highlighting of the essential features for an improved understanding of data

Data Models, Schemas, and Instances Schemas versus Instances Database Schema: The description of the database. It rarely changes. Includes descriptions of the database structure, data types, and the constraints on the database. Database Instance (snapshot): The actual data stored in a database at a particular moment in time. Changes rapidly. Every insert, delete, update will change the database state. Database Concepts6

Example SchemaInstance Database Concepts7

8 DB Internal Schema Internal Schema Conceptual Schema Conceptual Schema View 2 View n View 1 User 1 User 2 User n External Level Conceptual Level Internal Level Three-Schema Architecture

Data Models, Schemas, and Instances Three-Schema Architecture Defines DBMS schemas at three levels: External Level Describes that part of database that is relevant to a particular user. Users’ view of the database. The way perceived by end users. Conceptual Level Describes what data is stored in database and relationships among the data. The way perceived by the DBA & programmers. Internal Level Describes how the data is stored in the database. The way perceived by the DBMS & OS. Database Concepts9

Three-Schema Architecture 10 Internal Level Conceptual Level Struct STAFF { int Staff_No; char FName [15]; char LName [15]; date DOB; float Salary; int Bno; struct STAFF * next; }; External Level Staff_No FName LName DOB Salary Bno Staff_No FName LName Age SalaryStaff_No LName Bno View 1 View 2

Data Models, Schemas, and Instances Three-Schema Architecture Proposed to support DBMS characteristics of: Program-data independence. Support of multiple views of the data. Database Concepts11

Data Models, Schemas, and Instances -Mapping Database Concepts12 Mapping is the process of transforming requests and results between the Internal, Conceptual & External levels. Programs refer to an external schema, and are mapped by the DBMS to the internal schema for execution. Data extracted from the internal DBMS level is reformatted to match the user’s external view. Two types of mapping: – External / Conceptual mapping. – Conceptual / Internal mapping.

Data Models, Schemas, and Instances-Data Independence Data Independence is the ability to modify a schema definition in one level without affecting a schema definition in the next higher level. Two levels of data independence: – Logical data independence. – Physical data independence. Data Independent is similar to the concept of ADT in programming language where both hide the implementation details from the user. Database Concepts13

Database Concepts14 Internal Schema Internal Schema Conceptual Schema Conceptual Schema External Schema External Schema External Schema External Schema External Schema External Schema External/Conceptual Mapping Conceptual/Internal Mapping Logical data Independence Physical data Independence Data Independence in Three-Schema Architecture

Data Models, Schemas, and Instances Data Models Data Model: A set of concepts to describe the structure of a database, the operations for manipulating these structures, and certain constraints that the database should obey. Purpose of data modelling is to represent data in an understandable way. Categories of data models include: Conceptual data models (Object-based). Logical data models (Record-based). Physical data models. Database Concepts15

Data Models, Schemas, and Instances Categories of Data Models Conceptual data models: is the construction of an enterprise’s information that is independent of implementation details. Also called entity-based or object-based data models. Logical data models: is the logical description of an enterprise’s information with high level description of the implementation. Also called record-based data models. Physical data models: is the physical description of how data is stored in the computer. Database Concepts16

Categories of Data Models Database Concepts17 Physical model Physical model Logical model Logical model Conceptual model Conceptual model Hardware dependent Software dependent Hardware independent Software dependent Hardware independent Software independent

Data Models Conceptual Data Models (Object-Based): Entity-Relationship. Semantic. Functional. Object-Oriented. Logical Data Models (Record-Based): Relational Data Model. Network Data Model. Hierarchical Data Model. Physical Data Models. Database Concepts18

Data Models Database Concepts19 Staff_NoLNameSalaryBrn_No StreetTel_No St1 Name St2 Name St3 Name St4 Name Olayaa Malaz Rawda St1 Name1 7000Olayaa St2 Name St3 Name St4 Name Malaz Rawda Relational Data Model Network Data Model BranchStaff

Data Models Database Concepts20 St3 Name Hierarchical Data Model St1 Name1 7000St2 Name St4 Name Olayaa Malaz Rawda