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Geog 357: Data models and DBMS

Geographic Decision Making

Ways of storing digital data

• File structures– simple– ordered sequential– indexed

• Data models• Databases

– hierarchical– network– relational

File structures• Basic terms

– record• data items related to a single logical entity (e.g. a student

record) (row in a table)– field

• a place for a data item in a record (first name field in a student record) (column in a table)

– file• a sequence of records of the same type (the table)

File structures

3 Smith Jane A

1 Wood Bob C

2 Kent Chuck B

4 Boone Dan B

ID Last First Grade

record

fieldA file: “STUDENT”

File structures

• Simple list– 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

File structures• Search of a

simple list entails going through each record until search 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

File structures

• Ordered sequential files– 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

File structures

• Search of an ordered sequential list can use a binary search method - but only for the ordered field

1 Wood Bob C

2 Kent Chuck B

3 Smith Jane A

4 Boone Dan B

ID Last First Grade

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

Data models

• A data model is a particular way of conceptually organizing multiple data files in a database

– hierarchical– network– relational

Hierarchical data model

Class

Student

Grade

Instructor

ID

Parent-child relationship (one-to-one or one-to-many) among data

Department

Hierarchical data model

• Advantages

easy to search

can add new branches easily

• Disadvantages

must establish the types of search prior to development of the hierarchical structure

Network data model

Class

Student

Grade

Instructor

ID

One-to-one, one-to-many, many-to-one, or many-to-many relationships possible

Department

Network data model

Advantages

flexible, fast, efficient

Disadvantages

complex

restructuring can be difficult because of changing all the pointers

Data models

• Hierarchical and network data models have generally been replaced by the relational data model

• Relational databases (and their derivatives) dominate the (non-GIS) database market: Oracle, Informix

Databases

• A database is a collection of data files that is structured (organized) to facilitate data storage, manipulation, and retrieval.

• A database management system (DBMS) is a software package that performs these database functions

Why Databases??

• Shift from computation to information– Focus on the way to structure information

• Datasets increasing in diversity and volume. – Digital libraries, interactive video, e-commerce– ... need for DBMS exploding

• DBMS encompasses most of the information technology – OS, languages, theory, multimedia, logic, web

?

Database - Definition

• A very large, integrated collection of data. • A shared collection of logically related data

designed to meet the information needs of an organization

• Models real-world enterprise– Entities (e.g., students, courses)– Relationships (e.g., Madonna is taking CS564)

Database - Definition

• Three key elements of database definition:– Shared– Interrelated– Predefined applications

• Side notes:– Database is NOT the real world

• Database is an abstraction

– Database Information• Data becomes information only when they are used to provide

answers to queries

Database Management System (DBMS)

• DBMS: A software system that enables users to define, create, and maintain the database and which provides controlled access to this database.

• Provide a layer between user application programs and the data – Data Definition Language (DDL)– Data Manipulation Language (DML)

File-based Processing

Problems with File-based Systems

• Same data is stored in multiple places. Inconsistencies!Inconsistencies!

• We need to write special programs for each user question

• Data can be corrupted due to system crash while change is made.

• User programs are not easy to share data or evolve.

Database Management System

(DBMS)

Advantages of Database Approach

• Control of data redundancy– Have a central depository of all data and their

descriptions– Same information stored only once

• Data Integrity• Controlled access to database• Data independence• Concurrent Access• Crash recovery

Disadvantages of DBMS• Complexity• Cost of DBMS software, hardware and data conversion• Performance• Higher impact of a failure

When NOT to use DBMS?• No data sharing• Small scale• Real-time constraints

Roles in the Database Environment

• Data Administrator (DA)• Database Administrator (DBA)• Database Designers (Logical and Physical)• Application Programmers• End Users (native and sophisticated)

Summary• Databases are collections of inter-related data.• DBMS used to maintain, query large datasets.• Benefits include recovery from system crashes,

concurrent access, quick application development, data integrity and security.

• The advantages and disadvantages of DBMSs.• The personnel involved in the DBMS environment • Database management is one of the broadest,

most important areas in IST.