Presentation on the topic: “Database System Concepts and
Architecture”— Presentation Transcript: 1 Database System Concepts and Architecture
2 File-based approach schema Database approach Roles of database systems in the DBMS database environment Three-schema architecture and data independence Database languages Data models, Database schema and database status
Data Management Systems
Framework
Where are we? Extending database capabilities for new applications Suggested reading
: [1,2]: Chapters 1, 2 ) 2 3 File-based approach Data is
stored in one or more separate computer files Data is processed by computer programs – applications 3 4 File-based approach 4 5 File-based approach
Problems/limitations Data redundancyData inconsistency More details: see [2] 5
6 File-based approach File sharing approach
6 7 File-based approach File sharing
approachData (files) are shared between different applications Data redundancy issue is alleviated Resolves the problem of data inconsistency in different versions of the same file Other issues: Rigid data structure: If applications have to share files, the file structure that adapts to one application might not adapt to another. Physical data dependence: If the structure of the data file needs to be changed in any way, this alteration should be reflected in all application programs that use that data file No concurrency control support: While a data file is being processed by one application, the file will not be available to other applications or ad hoc queries 7
8 Schema File-based approach Approach Database Systems Database Systems Roles in the DBMS Database Environment Three-Schema Architecture and Data Independence Database Languages Data Models, Database Schema, and Data Management Systems Framework Database State Where are we? Extending database capabilities for new applications Suggested reading: [1,2]: Chapters 1, 2 8
9 The database approach arose because: Result: Data definition was integrated into application programs
, rather than stored separately and independently. No control over access and manipulation of data beyond that imposed by application programs Result: The database and database management system (DBMS). 9
10 Database approach
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Database approach dataKnown facts that can be recorded and have implicit meaning Information? Knowledge? More: Database: Shared collection
of logically related data and a description of this data, designed to meet an organization’s information needs 11 12 Database Approach System Catalog (
Metadata) provides a description of the data to enable independence of program data Related data logically comprise entities, attributes and relationships of an organization’s information. Database Management System (DBMS): a general-purpose software system that facilitates the processes of defining, building, manipulating, and sharing databases among multiple users and applications (or a software system that allows users to define, create, maintain, and control access to the
database) 12 13 Database approach Data definition language (
DDL)Allows you to specify data types, structures, and any data constraints that are stored in the database All specifications are stored in the Data Manipulation Language (DML) database. Query language: retrieve (query), update (insert, delete, modify) Controlled access to the database can include: a security system an integrity system a concurrency control system a recovery control system a user-accessible catalog Database system = database + DBMS software 13 14 Database Approach Functions
in the Database Environment Database administrator (DBA): responsible for authorizing access to the database, coordinating and monitoring its use, and acquiring software and hardware resources as needed Database designers: responsible for identifying the data to be stored in the database, choosing the appropriate structures to represent and store this data. Application Developers End Users Further
details: see [1,2]-chapter 1 15 DBMS components of the database approach
: See [1,2] for details 15 16
Database approach Characteristics of the database approach
Self-describing nature of a databasesystem Isolation between programs and data, and data abstraction Program data independence + Program operation independence = Data abstraction A Data model is a type of data abstraction Support for multiple views of the data Data exchange and multi-user transaction processing Other advantages of using the DBMS approach: see [1]-1.6 Self-descriptive nature of a database system: metadata Program data independence: structure data file, form access program. Independence of program operation: function and parameters 16 17
Database approach
History of database systemsFirst generation: Hierarchical and Network Second generation: Relational Third generation: Object-Relational, Object-oriented Brief history of database applications See [1]-section 1.7 Flat file databases: Data is stored in files consisting of one or more readable files, usually in text format. Hierarchical databases: Data is stored in tables with parent/child relationships with a strictly hierarchical structure. Network databases: Similar to the hierarchical model, but allows more flexibility; For example, a child table can be related to more than one parent table. Object-oriented databases: The object-oriented database model was developed in the late 1980s and early 1990s to deal with data types for which the relational model was not suitable. Medical and multimedia data, for example, required a more flexible system for data representation and manipulation. Object-relational databases: A hybrid model, combining features of object-oriented and relational models. 17 18
Network Model Schema Example
19 Relational Model Schema Example
20 File-Based Approach Schema Database ApproachDatabase System Roles in the DBMS Database Environment Three-schema architecture and data independence Database languages Data models, Database schema and database status Data Management Systems Framework Where are we? Extending database capabilities for new applications Reading tip: [1,2]: Chapters 1, 2 20 21
Three-schema architecture and data independence Objectives of the
three-schemaarchitecture All users must be able to access the same data Users should not need to know the details of the physical storage of the database DBA must be able to change the storage structures of the database of data without affecting user opinions The internal structure of the database must not be affected by changes in the physical aspects of storage DBAs must be able to change the conceptual structure of the database without affecting
all users 21 22 Three-schema architecture and data independence Three-tier architecture and data independence
22 23 Three-schema architecture and data independence
External level Users’ view of the database Describes the part of the database
that is relevant to a particular user. Conceptual level Community view of the database Describes where data is stored Database and relationships between data 23 24
Three-schema architecture and data independenceInternal level Physical representation of the database on the computer. Describes how
data is stored in the database 24 25 Three-schema architecture and data independence
25 26 Three-schema architecture and
data independence Data independence is the ability to change the schema at one level
of a database system without having to change the schema at the next higher level. Logical independence of data Refers to the immunity ofexternal schemas to changes in the conceptual schema Changes in the conceptual schema (e.g., adding/removing entities
) should not require changes to the external schema or rewrites of application programs 26 27
Three-schema architecture and independence Physical independence of data Refers to the immunity of the conceptual schema to changes in the internal schema Changes to the internal schema (e.g., using different file organizations, storage structures/devices) should not require changes to conceptual or external schemas 27
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Three-schema architecture and data independence 28 29 Schema File-based approach Database approach Roles of database systems in the
DBMS database environment Three-schema architecture and data independence Database languages Data models, database schema, and database state Data Management Systems Framework Where are we? Extending database capabilities for new applications Reading tip: [1,2]: Chapters 1, 2 29 30 Database languages
The Data Definition Language (
DDL) allows the DBA or user to describe and name entities, attributes, and relationships required by the application, as well as any associated integrity and security constraints Data Manipulation Language (DML) provides basic data manipulation operations in Data stored in the database Data Control Language (DCL) defines activities that are not in the categories of those for DDL and DML, such as granting privileges to users and defining when proposed changes to a database should be irrevocably made. 30 31 Database
languages Procedural DML allows the user
to tell the system exactly how to manipulate data (e.g. network and hierarchical DMLs) Non-procedural DML (declarative language) allows the user to indicate what data is needed rather than how it will be retrieved (e.g. SQL, QBE) Fourth generation languages (4GLs) Non-procedural languages: SQL, QBE, etc. Application generators, report generators, etc. (see [2]) 31 32
Schema File-basedapproach Database approach Database systems Roles in the DBMS database environment Three-schema architecture and data independence Database languages Data models, database schema, and database state Data Management Systems Framework Where are we? Extending database capabilities for new applications Reading Tip: [1,2]: Chapters 1, 2 32 33
Data models, database schema, and
database stateData model: An integrated collection of concepts for describing data, data relationships, and data constraints in an organization Data model categories include: Object-based ER (conceptual), object-oriented, … Record-based (representational) Relational, network, hierarchical Physical: used to describe data internally Describe data at the conceptual and external level 33 34
Data models, database schema, and database state Database schema: The description of a database
, which is specified during database design and is not expected to change frequently Schema diagram: a schema displayed Database status(snapshot):
the data in the database at a particular point in time 34 35 Schema File-based approach Database approach Database systems
Roles in the DBMS database environment Three-schema architecture and data independence Database languages Data models, Database schema and database status Data Management Systems FrameworkWhere are we? Expanding database capabilities for new applications Reading tip: [1,2]: Chapters 1, 2 35 36
Data
Management Systems FrameworkWhere are we? Visualization, Collaborative computing, Mobile computing, Knowledge-based systems Layer 3: Information extraction and sharing Data warehousing, data mining, Internet databases, collaboration, P2P, and network data management Layer 2: Interoperability and migration Heterogeneous database systems, client/server databases, multimedia database systems, Legacy database migration Layer 1: Database technologies Database systems, distributed database systems Networking, mass storage, agents, network computing infrastructure, Parallel and distributed processing, distributed object management Data Management Layer Application layer compatible with layer 36 37
Management Systems Framework of data Extension of database capabilities for new applications Example applications: storage and retrieval of images, videos, data mining (large amounts of data need to be stored and analyzed), spatial databases, time series applications, … Data structures more complex than relational representation New data types, except basic types of numeric and character strings New operations and query languages for new data types New storage and retrieval methods New security mechanisms … 37
38 Summary File-based approach Database approach Three-schemaarchitecture and data independence Database languages Data models Database schema and database state Data Management Systems Framework (Where are we?) Next week: ER Model 38
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Questions and Answers ? 39