INFS2608 Lecture 1 - Introduction
What is a data model?
"Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization." Purpose: To represent data in an understandable way.
What are Transaction Processing Monitors?
"Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP)."
What is a database?
"structured set of data" More specifically a shared collection of logically related data (comprised of entities attributes etc) Has a system catalog (metadata, data dict) to describe data to enable program-data independence
Basics of Three-level Architecture
- All users should be able to access same data. - Views are immune to changes made in other views. - Users don't need to know physical storage details. - DBA should be able to change database storage structures without affecting the users' views. - Internal structure of database should be unaffected by changes to physical aspects of storage. - DBA should be able to change conceptual structure of database without affecting all users.
File Based Systems
- Application programs for end users - Define & Manage own data
What is Three-Tier Client-Server
- By 1995, three layers proposed, each potentially running on a different platform. (presentation - business - data) Advantages three-tier: § 'Thin' client, requiring less expensive hardware. § Application maintenance centralized. § Easier to modify or replace one tier without affecting others. § Separating business logic from database functions makes it easier to implement load balancing. § Maps quite naturally to Web environment.
What is the Traditional Two-Tier Client-Server?
- Client (tier 1) manages user interface and runs applications. - Server (tier 2) holds database and DBMS. - Advantages include: § wider access to existing databases; § increased performance; § possible reduction in hardware costs; § reduction in communication costs; § increased consistency.
What are some issues with the Traditional Two-Tier Client-Server?
- Client side: § 'Fat' client, requiring considerable resources on client's computer to run effectively. § Significant client side administration overhead.
Disadvantages of DBMSs
- Complexity - Size - Cost (system, hardware, conversion to new sys) - Performance - Higher impact of a failure
What is a File-Server?
- Computer that acts as centralised storage station - File-server is connected to several workstations across a network. -Database resides on file-server. - DBMS and applications run on each workstation. - Disadvantages include: § Significant network traffic. § Copy of DBMS on each workstation. § Concurrency, recovery and integrity control more complex.
Advantages of DBMSs
- Control of data redundancy - Data consistency - More information from the same amount of data - Sharing of data - Improved data integrity - Improved security - Enforcement of standards - Economy of scale - Balance conflicting requirements - Improved data accessibility and responsiveness - Increased productivity - Improved maintenance through data independence - Increased concurrency - Improved backup and recovery services
Peoples & Roles in DB Env
- Data Administrator (DA) - Database Administrator (DBA) - Database Designers (Logical and Physical) - Application Programmers - End Users (naive and sophisticated)
What are the functions of a DBMS?
- Data Storage, Retrieval and Update. - A User-Accessible Catalog. - Transaction Support. - Concurrency Control Services. - Recovery Services. - Authorization Services. - Support for Data Communication. - Integrity Services. - Services to Promote Data Independence. - Utility Services.
Why database approach opposed to file-based approach?
- Data definition is stored separately & independently of programs (removes isolation & duplication) - Access & manipulation of data done by standardized language (i.e SQL) We thus get databases and DBMSs
Limitations of File-Based Approach
- Data is seperate and isolated (amongst end users) - Data is duplicated - Data-application dependence (file structure defined in program code) - Incompatible file formats (programs written in diff languages) - Fixed queries/proliferation of application programs (progs are written for specific needs -> new needs = new program)
What are the Levels of the ANSI-SPARC Three-Level Architecture?
- External Level = Users' view of the database (describes only parts of DB relevant to user) - Conceptual Level = Community view of the database. (Describes what data is stored in database their relationships) - Internal Level = Physical representation of the database on the computer. (Describes how the data is stored in the database.)
What is Teleprocessing?
- Traditional architecture. - Single mainframe with a number of terminals attached. - Trend is now towards downsizing.
What is big data?
- set of data analysis and predictive analysis techniques for large and complex sets of raw data (difficult or impossible to capture in ER models). - Uses machine learning and data mining techniques on raw data (instead of organizing data upfront into neat structures) - Exists because: § much larger set of data sources (e.g., Internet search/browsing, mobile devices) § much cheaper costs to store data (e.g., costs of hard disc drives reduced substantially) § growing interest in identifying patterns for business purposes (in all kinds of data)
What are the three main Multi-User DBMS Architectures?
1. Teleprocessing 2. File-server 3. Client-server
What are views?
Allow each user to have own view of DB View = a subset of database
What is conceptual schema & modelling?
Conceptual Schema: - Level between External & Internet - Conceptual schema is core that all user views rest upon. - Complete and accurate representation of an organization's data requirements. Conceptual modeling: - process of developing a model of information use that is independent of implementation.
What is DDL & DML?
DDL is Data Definition Language. - Used to define data structures & schemas. In SQL its shit like create table, alter table etc. - includes associated integrity and security constraints. DML is Data Manipulation Language. - Used to manipulate the data within a structure itself. In SQL it'd be shit like insert, update, delete Comprised of: Procedural DML (e.g., PL-SQL) - tells system exactly how to manipulate data. & Non-Procedural DML (e.g., SQL) - user to states exactly what data is needed rather than how it is to be retrieved.
What is a data model comprised of?
Data Model comprises: - a structural part; (operators to create) - a manipulative part; (operators to update/query) - possibly a set of integrity rules. "a description of data structure and the way data are organized using, for example, a database management system."
What is a system catalog?
Its a repository of information (metadata, data dictionary) describing the data in the database. - fundamental component of a DBMS. -Typically stores: § names, types, and sizes of data items; § constraints on the data; § names of authorized users; § data items accessible by a user and the type of access; § usage statistics.
Data Independence
Logical Data Independence: - immunity of external schemas (views) to changes in conceptual schema. - Changes to conceptual schema (i.e addition/removal of entities) should not require changes to external views or programs needing to be rewritten. Physical Data Independence: - immunity of conceptual schema to changes in the internal schema. - Internal schema changes (e.g. using different file organizations, storage structures/devices) should not require change to conceptual or external schemas.
Give example categories of data models
Object-based: § Entity-Relationship § Semantic § Functional § Object-Oriented. - Record-based: § Relational Data Model § Network Data Model § Hierarchical Data Model. - Physical
Benefits of Views
Reduce complexity (making views vs new tables) Provide a level of security (only see certain data) Mechanism to customise DB appearance Can be consistent regardless of how underlying DB changes
What is a Database Management System (DBMS)?
Software system that lets one: -Define -Create -Maintain -Control access to A database and its data. Middle man between requests from application program and the database itself.
