Relational Databases Lecture 2

Transcription

1 Relational Databases Lecture 2 Robb T Koether Hampden-Sydney College Fri, Jan 20, 2012 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

2 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

3 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

4 Benefits of Databases A few of the benefits of using a database: The user does not need to have knowledge of how the data is stored He works through a user-friendly interface Different users can be given different views of the data Each user may be unaware of the views that other users have Data can be easily shared among users Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

5 Benefits of Databases Online Catalog Sales Records Inventory Customer Salesman Manager Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

6 Benefits of Databases Comprehensive Database (Catalog, Sales, Inventory) Customer Salesman Manager Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

7 Various Roles Roles of various individuals involved The database administrator (DBA) Oversees the entire system The database designer Designs a database to meet the specs The user Queries the database according to his needs At various times in this course, we will be the database designer and the database user Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

8 Various Roles Roles of various individuals involved The database administrator (DBA) Oversees the entire system The database designer Designs a database to meet the specs The user Queries the database according to his needs At various times in this course, we will be the database designer and the database user One other person involved is the person who built the DBMS Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

9 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

10 Concurrency Multiple users accessing the very same data at the very same time leads to the concurrency problem For example, Alice, a customer, requests the price of item #123 At the very same time, Bob, an employee, is updating the price of item #123 Which price will Alice see? Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

11 Concurrency Multiple users accessing the very same data at the very same time leads to the concurrency problem For example, Alice, a customer, requests the price of item #123 At the very same time, Bob, an employee, is updating the price of item #123 Which price will Alice see? It depends on who goes first, Alice or Bob Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

12 Concurrency More significantly, Alice, an airline employee goes online to select a list of passengers on flight #123 At the very same time, Bob, another airline employee, goes online to change the flight number from #123 to #456 Alice selects the first 50 names of passengers on flight #123 At that moment, the flight number is changed to #456 The last 50 names are not selected because the flight number was no longer #123 This type of conflict must be avoided Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

13 OLAP Most database applications fall into one of two categories: OLAP or OLTP Definition (Database) Online analytical processing (OLAP) involves querying a database to obtain summary data, typical retrievals and aggregation A typical OLAP application would be to get the total daily sales from online purchases OLAP is computationally intensive (eg, summing over millions of records) This is more like what we will do when we first study databases Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

14 OLTP Definition (Database) Online transaction processing (OLTP) involves many small queries, typically insertions A typical OLTP application would be a database of online purchases Each purchase is inserted into the database OLTP is not computationally intensive This is more like what we will do with PHP and Javascript Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

15 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

16 Types of Databases Originally, databases were simply collections of data, arranged in whatever way the programmer saw fit The DBMS was simply a program that could process the data Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

17 Types of Databases In the early 1970s, the concept of a relational database (RDB) was introduced Its data were organized into tables of rows and columns Queries were organized into select, insert, delete, and update Given the standardized forms, queries could be highly optimized by the DBMS Today, SQL (Structured Query Language) is the standard for relational databases Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

18 Types of Databases Item Price Stock Cust Item Qty Alice Bob : : : : : : 2 4 Catalog of Items Sales A Relational Database (SQL) Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

19 Types of Databases More recently, other forms have appeared, most notably Extensible Markup Language (XML) An XML database is structured hierarchically The underlying theory is less mature The supporting software is less extensive The queries are less optimized On the other hand, the structure is much more flexible Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

20 Types of Databases Company Catalog Sales Item1 Item2 Cust1 Cust2 Price Stock Item Qty A Hierarchical Database (XML) Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

21 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

22 Relational Databases A relational database is a database in which the data are stored in tabular form, arranged in rows and columns Traditionally, rows are called records and columns are called fields In modern terminology, rows are called tuples and columns are called attributes Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

23 Relational Databases Consider a database of courses Courses table Dept Number Title Credit COMS 480 Databases 3 MATH 121 Statistics 4 CHEM 110 Chemical Concepts 3 COMS 331 Computer Graphics 3 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

24 Relational Databases In the example, the tuples are ( COMS, 480, Databases, 3) ( MATH, 121, Statistics, 4) etc The attributes are Dept Number Title Credit Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

25 Relational Databases The table expresses a relation, namely The department dept offers a course numbered number with the title title for credit hours of credit For example, the first row represents the statement The department COMS offers a course numbered 480 with the title Databases for 3 hours of credit Thus, each tuple of the database represents a true statement, an instance of the relation Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

26 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

27 Relational Databases A query is a request that is sent to the DBMS The DBMS parses the query, optimizes it, and sends it to the storage engine, which executes the query on the database There are four basic types of query Select Insert Delete Update Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

28 Relational Databases A selection query might request all COMS courses The result would be Dept Number Title Credit COMS 480 Databases 3 COMS 331 Computer Graphics 3 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

29 Relational Databases An insertion query might add the tuple ( COMS, 261, Computer Science I, 4) The result would be Dept Number Title Credit COMS 480 Databases 3 MATH 121 Statistics 4 CHEM 110 Chemical Concepts 3 COMS 331 Computer Graphics 3 COMS 261 Computer Science I 4 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

30 Relational Databases A deletion query might delete the tuple ( COMS, 261, Computer Science I, 4) The result would be Dept Number Title Credit COMS 480 Databases 3 MATH 121 Statistics 4 CHEM 110 Chemical Concepts 3 COMS 331 Computer Graphics 3 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

31 Relational Databases An update query might change COMS to CSCI The result would be Dept Number Title Credit CSCI 480 Databases 3 MATH 121 Statistics 4 CHEM 110 Chemical Concepts 3 CSCI 331 Computer Graphics 3 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

32 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

33 Schemas Definition (Schema) A relation schema consists of the relation s name, a list of its attributes, and their domains, ie, the set of legitimate values of each attribute A database schema is a set of relation schemas Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

34 Schemas The schema of the Courses relation is Courses(Dept string, Number integer, Title string, Credit integer) More specifically, 100 Number Credit 4 Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

35 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

36 Primary Keys Every table must have a primary key The primary key is an attribute whose value is unique for each tuple Or it is a set of attributes whose combination of values is unique for each tuple Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

37 Primary Keys In the Courses table, the key would be the (Dept, Number) combination In a relation schema, we underline the attributes that comprise the primary key We represent the schema as Courses(Dept string, Number integer, Title string, Credit integer) Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

38 Outline 1 Databases Systems 2 The Concurrency Problem 3 Types of Databases 4 Relational Databases 5 Queries 6 Schemas 7 Primary Keys 8 Assignment Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36

39 Assignment Read Chapter 2 - Database System Concepts and Architecture Look over the Review Questions and Exercises at the end the chapter Robb T Koether (Hampden-Sydney College) Relational DatabasesLecture 2 Fri, Jan 20, / 36