CS4222 Principles of Database System 3/24/2018 CS4222 Principles of Database System 1. Introduction Huiping Guo Department of Computer Science California State University, Los Angeles

Some concepts Database Data Database Management System (DBMS) Fall 2005 Some concepts Database A very large, integrated collection of data. Data Known facts that can be recorded and have an implicit meaning Database Management System (DBMS) a software package that enables users to create and maintain databases Facilitates the processes of defining, constructing, manipulating, and sharing databases among various users and applications Database System: The DBMS software together with the data itself. Sometimes, the applications are also included. 1. Introduction CS4222_Summer'17

Simplified database system environment 1. Introduction CS4222_Summer'17

Typical DBMS Functionality Define a particular database in terms of its data types, structures, and constraints Construct or Load the initial database contents on a secondary storage medium Manipulating the database: Retrieval: Querying, generating reports Modification: Insertions, deletions and updates to its content Accessing the database through Web applications Processing and Sharing by a set of concurrent users and application programs – yet, keeping all data valid and consistent 1. Introduction CS4222_Summer'17

Typical DBMS Functionality Other features: Protection or Security measures to prevent unauthorized access “Active” processing to take internal actions on data Presentation and Visualization of data Maintaining the database and associated programs over the lifetime of the database application Called database, software, and system maintenance 1. Introduction CS4222_Summer'17

Example of a Database Miniworld Mini-world for the example: A database represents some aspect of the real world Mini-world for the example: Part of a UNIVERSITY environment. Some mini-world entities: STUDENTs COURSEs SECTIONs (of COURSEs) (academic) DEPARTMENTs INSTRUCTORs 1. Introduction CS4222_Summer'17

Example of a Database (with a Conceptual Data Model) Some mini-world relationships: SECTIONs are of specific COURSEs STUDENTs take SECTIONs COURSEs have prerequisite COURSEs INSTRUCTORs teach SECTIONs COURSEs are offered by DEPARTMENTs STUDENTs major in DEPARTMENTs Note: The above entities and relationships are typically expressed in a conceptual data model, such as the ENTITY-RELATIONSHIP data model (to be discussed in details later) 1. Introduction CS4222_Summer'17

Example of a simple database 1. Introduction CS4222_Summer'17

Main Characteristics of the Database Approach Self-describing nature of a database system: A DBMS catalog stores the description of a particular database (e.g. data structures, types, and constraints) The description is called meta-data. This allows the DBMS software to work with different database applications. 1. Introduction CS4222_Summer'17

Example of a simplified database catalog 1. Introduction CS4222_Summer'17

Main Characteristics of the Database Approach (continued) Insulation between programs and data: Called program-data independence. Allows changing data structures and storage organization without having to change the DBMS access programs The characteristic that allows program-data independence is called data abstraction Support of multiple views of the data: Each user may see a different view of the database, which describes only the data of interest to that user. 1. Introduction CS4222_Summer'17

Main Characteristics of the Database Approach (continued) Sharing of data and multi-user transaction processing: Allowing a set of concurrent users to retrieve from and to update the database. Concurrency control within the DBMS guarantees that each transaction is correctly executed or aborted Recovery subsystem ensures each completed transaction has its effect permanently recorded in the database OLTP (Online Transaction Processing) is a major part of database applications. This allows hundreds of concurrent transactions to execute per second. 1. Introduction CS4222_Summer'17

Database Users Users may be divided into Those who actually use and control the database content, and those who design, develop and maintain database applications (called “Actors on the Scene”) Those who design and develop the DBMS software and related tools, and the computer systems operators (called “Workers Behind the Scene”). 1. Introduction CS4222_Summer'17

Database Users Actors on the scene Database administrators: Responsible for authorizing access to the database, for coordinating and monitoring its use, acquiring software and hardware resources, controlling its use and monitoring efficiency of operations. Database Designers: Responsible to define the content, the structure, the constraints, and functions or transactions against the database. They must communicate with the end-users and understand their needs. 1. Introduction CS4222_Summer'17

Advantages of Using the Database Approach Controlling redundancy in data storage and in development and maintenance efforts. Restricting unauthorized access to data. Providing Storage Structures (e.g. indexes) for efficient Query Processing Providing persistent storage for program Objects 1. Introduction CS4222_Summer'17

Advantages of Using the Database Approach (continued) Providing backup and recovery services. Providing multiple interfaces to different classes of users. Representing complex relationships among data. Enforcing integrity constraints on the database. Permitting inferences and actions using deductive and active rules 1. Introduction CS4222_Summer'17

File systems vs a DBMS Scenario A university wishes to store large collection of data on faculty, departments, students, and so on The data will be accessed by different faculty, departments, students for various reasons 1. Introduction CS4222_Summer'17

Storing the data in files (cont.) Goal Find the names of all faculty in a department Solution Write a procedure to search files for matching faculty Problems -query is hard-coded, requires program -new queries require re-programming -no theory for query optimization 1. Introduction CS4222_Summer'17

Storing the data in files (cont.) Goal: Data should be free of inconsistencies A student cannot get both B and A in the same course Solution make sure procedures verify data is valid Problems: integrity constraints cannot be found or changed without re-programming 1. Introduction CS4222_Summer'17

Storing the data in files (cont.) Goal Data should be secure from unauthorized users Solution use file access permissions Problems: host OS may not provide any file access restrictions file access permission provided by host operating system will be inadequate 1. Introduction CS4222_Summer'17

Database solution Create an application to which we input: what our data will look like what constraints apply to the data allows us to pose arbitrary queries allows us to specify access controls monitors modification of data The database is generic works with anyone’s data or queries -at run time 1. Introduction CS4222_Summer'17

Describing and Storing Data in a DBMS Fall 2005 Describing and Storing Data in a DBMS data model Data can be represented in different ways Trees, graphs, tables, etc. A data model is a way to represent data relational data model using tables to represent data 1. Introduction CS4222_Summer'17 5

Relational data model Relation Schema A table with rows and columns. Conceptual schema (logical schema) Describes the columns, or fields of relations Physical schema File organizations Indices External schema A collection of views from the conceptual schema 1. Introduction CS4222_Summer'17

Levels of Abstraction View 1 View 2 View 3 Conceptual Schema Fall 2005 Levels of Abstraction View 1 View 2 View 3 Conceptual Schema Physical Schema disk Schemas are defined using DDL; data is modified/queried using DML. 1. Introduction CS4222_Summer'17 6

Example: University Database Fall 2005 Example: University Database Conceptual schema: Courses(cid: string, cname:string, credits:integer) Faculty(fid:string, fname:string, sal:real) Teaches(cid:String, fid:string) Physical schema: Relations stored as unordered files. Index on first column of Students. External Schema (View): Course_info(cid:string,fname:string) 1. Introduction CS4222_Summer'17 7

Fall 2005 Data Independence * Applications insulated from how data is structured and stored. Logical data independence Protection from changes in logical structure of data. Physical data independence Protection from changes in physical structure of data. One of the most important benefits of using a DBMS! 1. Introduction CS4222_Summer'17

Logical data independence example Suppose logical schema has been changed Faculty_public(fid:string, fname:string, office:string) Faculty(fid:string, sal:real) Need to change the definition of the view course_infor The applications that use Course_infor remain the same 1. Introduction CS4222_Summer'17

Queries in a RDBMS Relational calculus Relational algebra A formal query language based on mathematical logic Relational algebra Anther formal language based on a collection of operators for manipulating relations Structured Query Language (SQL) Data Manipulation language (DML) Data Definition Language (DDL) 1. Introduction CS4222_Summer'17

What will be covered Database design Database Implementation Data modeling Entity-Relationship (ER) model ER diagram  relational model Normalization Database Implementation Data Definition Language (DDL) Authorization Integrity constraints Stored procedures and triggers 1. Introduction CS4222_Summer'17

What will be covered Query Languages Application Development Relational calculus and algebra DML queries, subqueries, nested queries, joins Application Development Embedded SQL JDBC 1. Introduction CS4222_Summer'17