Overview of Database Management Systems - Operations and ...

Overview of Database Management Systems

• Goals: – DBMS basic concepts – Introduce underlying managerial issues – Prepare for discussion of uses of DBMS, such as OLAP and database mining

misnotes-dbms-19980121.ppt

Steven O. Kimbrough

1

Overview of Database Management • What is a database system? – Acomputerized record-keeping system

• Record? – Think of it as a row in a table, consisting of fields of data – Note: Role of metaphors

• System? – A general software module that provides all sorts of services: – Create new files and add them to the database – Insert new data into an existing file – Retrieve data from existing files – Update (change) data in existing files – Delete data in existing files – Delete (remove) existing files from the database – And much else: system management features, security, integrity, etc.


Steven O. Kimbrough

2

Overview of Database Management • Important and fundamental distinctions – System software vs application software – Logical vs physical » See MIS Notes, chapter 1

• System software, e.g., – – – –

Operating system Language compilers Communications DBMS

• Idea: everybody needs it, so write it once and standardly for all – Reading/writing files (OS) – Storing/retrieving records (DBMS)


Steven O. Kimbrough

3

Overview of Database Management • Where do database systems come from? – Commercial software vendors » Oracle, DB2, RDB, Ingres, Focus, etc. for mainframes » For Unix, Oracle, Ingres, Informix, etc. » Macs: Mainly Oracle » PCs: Access, Paradox, Oracle, etc.

• Is there more than one kind? Why? – Yes: flat file systems, network systems, hierarchical systems, relational systems, object-oriented systems – And different brands for each type – Why? History, needs and requirements

• Is there a standard? Yes, 2 really – Relational DBMS – SQL as the access language » DDL, DML, etc. » Note: Can have SQL w/o relational and relational w/o SQL – Note: Access is relational & has SQL access misnotes-dbms-19980121.ppt

Steven O. Kimbrough

4

Overview of Database Management • Who uses database systems? – – – –

Everyone, high, middle, and low Pervasive in business and commerce Difficult to overestimate importance Quite possible to earn your way through school doing database work

• Are databases here to stay? Are they stable? – Here to stay? Absolutely! – Stable? Yes, but... » Relational DBMS with SQL: commercial de facto standard; client-server uses » Object-oriented DBMS: thought to be the next big thing • • •

A few years away Specialized uses SQL will stay---probably


Steven O. Kimbrough

5

More Comments on Database and Information Systems Generallly • Important concepts/themes • Persistence – Why we need data bases

• Metaphors and computing generally and database specifically – Relational model, relational databases: » Tables, tables, tables

• Indirection – e.g. external, conceptual, internal views of database


Steven O. Kimbrough

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Overview of Database Management •

Why database?

•

Alternatives are unattractive

•

Positive reasons for DBMSs •

Data independence

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Reduction of redundancy

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Avoidance of inconsistency

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Enforcement of standards

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Security

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Integrity

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Use of markets


Steven O. Kimbrough

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Database Architecture • • • •

•

These comments apply broadly to all types of DBMSs ...but, will focus on SQL, "big guys" systems ANSI/SPARC (broadly accepted) framework Three levels: • External • Conceptual • Internal "Relational" refers to how the data appears to users, so to the external and conceptual levels – How it appears (as tables) and – How you operate on it – Recall: metaphors


Steven O. Kimbrough

8

The External Level •

The individual user level (application programmer, someone interacting online with the database, or an application, or a user via a nice front end)

•

Users (typically) interact with a DBMS using a language of some sort. • e.g., SQL, either embedded in a programming language or interactively • e.g., QBE for users

•

Data sublanguage vs host language

•

Data sublanguage: • Data definition language (DDL) • Data manipulation language (DML)

•

The point of external views: to give different users different views of the data – Views: concept, advantages


Steven O. Kimbrough

9

The Conceptual Level •

A "representation of the entire information content of the database"

•

...from the point of view of the underlying data model (here, relational)

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Conceptual schema

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Conceptual schema is to be "pure"; no refernce to the physical


Steven O. Kimbrough

10

The Internal Level •

Described by the internal schema

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Refers to details of the physical representation – E.g., how records are laid out on a hard drive

•

But NOT to device-specific physical details


Steven O. Kimbrough

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The Database Administrator •

Data administrator---makes strategic and policy decisions

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Database administrator---technical support for implementing policy decisions •

Defines internal schema

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Liaison with users

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Oversees and defines security and integrity checks

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Manages backup and recovery

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Performance monitoring, database tuning


Steven O. Kimbrough

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The Parts-Supplier Database •

Three tables: S (suppliers), P (parts), SP

S S# SNAME STATUS CITY ====================================== S1 S2 S3 S4 S5

Smith Jones Blake Clark Adams

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Table (and relation)

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Tuple (or record)

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Field

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Attribute

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Domain

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Data types

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Data atomicity

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Key, key field


20 10 30 20 30

London Paris Paris London Athens

Steven O. Kimbrough

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The Parts-Supplier Database (continued) P P# PNAME COLOR WEIGHT CITY ====================================== P1 P2 P3 P4 P5 P6

Nut Bolt Screw Screw Cam Cog

Red Green Blue Red Blue Red

12 17 17 14 12 19

London Paris Rome London Paris London

•

Ordering on the rows?

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Does CITY in P mean the same as CITY in S?

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17 what? Pounds? Ounces? Tons? Kilograms?

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Why more than one table?

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How do we answer queries that rely on data in more than one table?


Steven O. Kimbrough

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The Parts-Supplier Database (continued) SP S# P# QTY ====================================== S1 S1 S1 S1 S1 S1 S2 S2 S3 S4 S4 S4

P1 P2 P3 P4 P5 P6 P1 P2 P2 P2 P4 P5

300 200 400 200 100 100 300 400 200 200 300 400

•

S5? S6?

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Double key, S#-P#

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Why more than one table?

•

How do we answer queries that rely on data in more than one table?


Steven O. Kimbrough

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