IST Databases and DBMSs Todd S. Bacastow January 2005

IST 210 Evolution

IST 210 Ways of storing data Files (1960) (ancient times) Databases Hierarchical (1970) Network (1970) Relational (1980) Object (1990)

IST 210 File terms Record data items related to a single logical entity (e.g. a student’s information) or row in a table Field a place for a data item in a record (first name field in a student record) or a column in a table File a sequence of records of the same type (the table)

IST 210 File structures 3 Smith Jane A 1 Wood Bob C 2 Kent Chuck B 4 Boone Dan B ID Last First Grade record field A file: “STUDENT”

IST 210 File organization Serial new records appended Sequential records ordered in file, usually according to a numeric key

IST 210 File structures Serial list of entries in which the order of entry into the list determines the order of the list 3 Smith Jane A 1 Wood Bob C 2 Kent Chuck B 4 Boone Dan B ID Last First Grade

IST 210 File structures Search of a simple list entails going through each record until the query is satisfied (linear search), which is inefficient 3 Smith Jane A 1 Wood Bob C 2 Kent Chuck B 4 Boone Dan B ID Last First Grade

IST 210 File structures Sequential list of entries ordered in some way (e.g. numerically or alphabetically) 1 Wood Bob C 2 Kent Chuck B 3 Smith Jane A 4 Boone Dan B ID Last First Grade

IST 210 File structures Search of an ordered sequential list can use a search method 1 Wood Bob C 2 Kent Chuck B 3 Smith Jane A 4 Boone Dan B ID Last First Grade

IST 210 File structures Indexes provide a reference to records based on an index field, which is ordered Boone * Kent * Smith * Wood * 1 Wood Bob C 2 Kent Chuck B 3 Smith Jane A 4 Boone Dan B ID Last First GradeLast Pointer

IST 210 Problems with files Redundancy number of files grows with applications, and data is duplicated Inconsistency data is updated in one application’s files, but not in another’s Maintenance problems changes to data structures mean changes to many programs Difficulty combining data business needs may mean users want data from different applications

IST 210 Other ways to organize Data model A data model is a particular way of conceptually organizing multiple data files in a database Other common models Hierarchical Network Relational Object

IST 210 Network model

IST 210 Network data model Relationships: one-to-one one-to-many many-to-one many-to-many Class Student Grade Instructor ID Department

IST 210 Network data model Advantages flexible, fast, efficient Disadvantages Complex Restructuring can be difficult because of changing all the pointers

IST 210 Hierarchical database model

IST 210 Hierarchical data model Parent-child relationship: one-to-one one-to-many Class Student Grade Instructor ID Department

IST 210 Hierarchical data model Advantages easy to search add new branches easily Disadvantages Must establish the types of search prior to development of the hierarchical structure

IST 210 Summary Hierarchical and network data models have generally been replaced by the relational data model Relational databases dominate the database market Oracle Informix SQL Server DB2 ……..

IST 210 Relational database model Stores both Data about real world objects (entities) in tables Relationships between the tables

IST 210 Relational database Fields (columns) in the table store attributes. Each attribute has a specific domain. Tuples (or records or rows) in the table store information. Each tuple is a unique instance of an object. Tables are composed of a set of tuples. A table is also called a relation.

IST 210 Terms Table A collection of relevant data relating to one type of real world objects. Column A specific place for one type of data relating to one type of real world objects. Domain Set of all possible values for a specific column. Row Collection of data describing one real world object. Primary Key Columns, which are part of the row and uniquely identify any one row.

IST 210 Records Each record represents a logical entity (e.g. a student) Each field represents an attribute of the logical entity 1 Wood Bob C IST357 2 Kent Chuck B IST115 3 Smith Jane A IST357 4 Boone Dan B IST357 ID Last First Grade Class Student

IST 210 Keys Each table has a primary key, one field (or a combination of fields) that has a unique value for each and every record in the table ID is the primary key in this table (two students may share either a last or first name) 1 Wood Bob C IST357 2 Kent Chuck B IST115 3 Smith Jane A IST357 4 Boone Dan B IST357 ID Last First Grade Class Student

IST 210 Relating tables Tables can be related (joined) together based on their keys The idea is to decompose into separate tables with no redundancy and to provide a capability to reassemble with no information loss 1 Wood Bob C IST357 2 Kent Chuck B IST115 3 Smith Jane A IST357 4 Boone Dan B IST357 ID Last First Grade Class Student IST Jones IST Brower IST Fountain Class Name #Stud Instructor

IST 210 Relating tables 1 Wood Bob C IST357 2 Kent Chuck B IST115 3 Smith Jane A IST357 4 Boone Dan B IST357 ID Last First Grade Class Student IST Jones IST Brower IST Mennis Class Name #Stud Instructor Primary key Foreign key

IST 210 Relating tables 1 Wood Bob C IST357 2 Kent Chuck B IST115 3 Smith Jane A IST357 4 Boone Dan B IST357 ID Last First Grade Class Student IST Brower IST Jones IST Jones Class Name #Stud Instructor Jones 332 Brower 517 Instructor Name Office

IST 210 DBMS Schema Ultimately data in databases is stored in files, but their structure is hidden Conceptual Schema External Schema Internal Schema The view on data used by application programs. The logical model of data that is separate from how it is used. The physical storage of data in files and indexes.

IST 210 RDBMS Features Data Definition Language (DDL) Data Manipulation Language (DML) Integrity Constraints Transaction Management Concurrency Security Tuning of Storage

IST 210 Data integrity and validation (Constraints)

IST 210 Relationships Link between entities. A relationship may define constraints. E.G, a person can only have one SSN.

IST 210 Advantages of RDBMS Eliminate unnecessary duplication of data Enforce data integrity through constraints Changes to conceptual schema need not affect external schema Changes to internal schema need not affect the conceptual schema Many tools are available to manage the database

IST 210 Disadvantages of RDBMS To store objects (e.g., drawings) in a relational database, the objects have to be ‘flattened’ into tables e.g., a digital representation of a parcel must be separated from the behaviour of other parcels Complex objects have to be taken apart and the parts stored in different tables When retrieved from the database, the object has to be reassembled from the parts in different tables

IST 210 Other Types of DBMS Object DBMS store objects as objects designed to handle complex nested objects for graphical and multimedia applications Object-relational DBMS hybrid databases that can store data in tables but can also store objects in tables

IST 210 Object DBMS ODBMS have the advantage that objects can be stored directly Object databases are closely linked to programming languages with ways of navigating through the database

IST 210 Summary Common word Textbook word Alternate word Object word TableRelationFile or Data set (old) Object class ColumnAttributeFieldObject field Domain Range of possible values Datatype, subtype RowTupleRecordObject instance Primary key Key of the record Object identifier