Database System Concepts and Architecture Chapter 2 COSC 457 Sungchul Hong

The architecture of DBMS Early monolithic system Modular design Client module Server module Storage, access, search, and other functions

Data Models, Schemas, and Instances A collection of concepts that can be used to describe that structure of a database. Structure of a database: data types, relationships, and constraints Basic operations Specifying retrievals and updates on the database Dynamic aspect (behavior): user defined operations.

Categories of Data Models High-level (conceptual) Data Models They provide concepts that are close to the way many users perceive data. Representational (Implementation) Data Models Between two extremes Low-level (physical) Data Models They provide concepts that describe the details of how data is stored in the computer.

Conceptual Data Model Entities, attributes, and relationships Entity represents a real-world object or concept. An attribute represents some property of interest that further describes an entity. A relationship among two or more entities represents an interaction among the entities. Entity-Relationship model.

Representational Data Models Relational data model Network models Hierarchical models Object data models

Hierarchical Model ADVANTAGES: DISADVANTAGES: Hierarchical Model is simple to construct and operate on Corresponds to a number of natural hierarchically organized domains - e.g., assemblies in manufacturing, personnel organization in companies Language is simple; uses constructs like GET, GET UNIQUE, GET NEXT, GET NEXT WITHIN PARENT etc. DISADVANTAGES: Navigational and procedural nature of processing Database is visualized as a linear arrangement of records Little scope for "query optimization"

Network Model ADVANTAGES: DISADVANTAGES: Network Model is able to model complex relationships and represents semantics of add/delete on the relationships. Can handle most situations for modeling using record types and relationship types. Language is navigational; uses constructs like FIND, FIND member, FIND owner, FIND NEXT within set, GET etc. Programmers can do optimal navigation through the database. DISADVANTAGES: Navigational and procedural nature of processing Database contains a complex array of pointers that thread through a set of records. Little scope for automated "query optimization”

Network Model

Relational Data Model Advantages Disadvantage Strong Mathematical background Query optimization is possible 4th generation language (non-procedural) Disadvantage Some (e.g. joint) Operations require a great amount of resources.

Relational Data Model N Branch Work 1 Staff

Physical Data Models How data is stored in the computer by representing information such as record formats, record orderings, and access paths.

Schemas, Instances, and Database State Schema (Meta data, intension) The description of the database It is specified during database design. It is not expected to change frequently. Schema diagram: names of record types and data items Instances (extension of the schema) The actual data in a database It may change quite frequently. Database state: a snapshot, current set of instances DBMS is responsible for ensuring that every state of the database is a valid state.

Schema Instance

DBMS Architecture and Data Independence The Three-Schema Architecture Internal level Conceptual level External level Data Independence Logical data independence Physical data independence

The Three-Schema Architecture Internal level (internal schema) Physical storage structure of the database. Conceptual level (conceptual schema) The structure of the whole database for a community of users. Hides details External (view) level (external schemas or user views) User’s view point of a database. Mappings: transforming requests and results between levels

Data Independence Logical data independence Physical data independence Capacity to change the conceptual schema without having to change external schemas or application programs. Physical data independence Capacity to change the internal schema without having to change to conceptual (or external) schema. Only mappings between two levels will be changed.

DBMS Languages Data Definition Language (DDL) Storage Definition Language (SDL) View Definition Language (VDL) Data Manipulation Language (DML) Comprehensive database language  SQL Nonprocedural DML Interactive (query language) or embedded (host/data) Set-at-a-time, set-oriented, declarative (what) Procedural DML Embedded in a general-purpose programming language. Record-at-a-time,

SQL Example (DDL) CREATE TABLE DEPT ( DNAME VARCHAR(10) NOT NULL, DNUMBER INTEGER NOT NULL, MGRSSN CHAR(9), MGRSTARTDATE CHAR(9), PRIMARY KEY (DNUMBER), UNIQUE (DNAME), FOREIGN KEY (MGRSSN) REFERENCES EMP ON DELETE SET DEFAULT ON UPDATE CASCADE );

SQL Example (DML) SELECT BDATE, ADDRESS FROM EMPLOYEE WHERE FNAME='John' AND MINIT='B’ AND LNAME='Smith’;

SELECT staffNo, fName, lName, position, salary FROM Staff sex DOB salary branchNo SL21 John White Manager M Oct/1/45 30000 B005 SG37 Ann Beech Assistant F Nov/10/60 12000 B003 SG14 David Ford Supervisor Mar/24/58 18000 SA9 Mary Howe 19/Feb/70 9000 B007 SG5 Susan Brand Jun/3/40 24000 SL41 Julie Lee Jun/13/65 SELECT staffNo, fName, lName, position, salary FROM Staff WHERE salary > 10000;

DBMS Interfaces Menu-Based Interfaces for Browsing. Browsing interface Forms-Based Interfaces Forms specification languages Graphical User Interfaces Natural Language Interface Interfaces for Parametric Users Bank tellers Interfaces for the DBA: privileged commands Creating accounts, setting system parameters, granting account authorization, changing a schema, …

DBMS Component Modules Operating systems Stored Data Manager DDL compiler Stores description of the schemas in the DBMS catalog. Names of files, data items, storage details of each file, mapping in formations among schemas, constraints Run-time database processor Query compiler: interactive queries Pre-compiler: DML command from an application program DML compiler: compilation into object code.

Embedded Code (Java) try { rset= stmt.executeQuery("SELECT * from department"); ResultSetMetaData rsmd=rset.getMetaData(); while (rset.next()) { System.out.println(" " + rset.getString(1) + " " + rset.getString(2) + " " + rset.getString(3) +" "); }

Interactive SQL SQL> SELECT table_name FROM user_tables; TABLE_NAME ------------------------------ DEPARTMENT STUDENT

Database Systems Utilities Loading Convert non-database files into db files Backup File reorganization organize a database file into a different file organization to improve performance Performance monitoring Monitoring database usage. Sorting files, data compression, etc.

Tools, Application Environments, and Communication Facilities Expanded data dictionary system Usage standards, application program descriptions Application development environment Communications software

Classification of Database Data model Relational data model, Object data model, Hierarchical, Network Number of users Single-user (Access) , multi-user systems (Oracle) Number of sites Centralized, distributed Costs Types of Access path Target area General purpose, special purpose (on-line transaction processing system)