database management system

Data Bases : 

Data Bases

Chapter 8 Homework… : 

Chapter 8 Homework… 9, logical records cannot be separated by dividing the file into blocks of fixed length. Instead, some other technique for separating records must be used. One approach, use a special symbol sequence to indicate the end of one logical record and beginning if the next. 12, Segment 3, Segment 1, Segment 4, Segment 3 20, Probability of three records hashing to different locations is (10/10)(9/10)(8/10)=.72, therefore probability of two hashing to same location is 1 - .72 or .28 If fourth record added, chances of at least two hashing to same location is 1 – (1x .9 x .8 x .7) or .496 30, XY in ASCII (8bits/symbol) 01011000 01011001, binary of 35317/41 leaves remainder of 16.

Databases – getting started… : 

Databases – getting started… Definitions: What’s yours? Organized so its contents can easily be accessed, managed, and updated. The most prevalent type of database is the relational database (EF Codd – 70’s), a tabular database in which data is defined so that it can be reorganized and accessed in a number of different ways. Most common form of access to the data: SQL (structured query language) A distributed database is one that can be dispersed or replicated among different points in a network. An object-oriented programming database is one that is congruent with the data defined in object classes and subclasses.

Databases – getting started… : 

Databases – getting started… Popular Today? Why? Who? Advantages / Disadvantages) Vendors? SQL Server, DB2, Oracle, Peoplesoft, MySQL... Historical perspective – file vs database organization –

File versus Database Organization : 

File versus Database Organization Are there advantages to File Organization? Security, etc. Disadvantages?

Slide 6: 

File versus Database Organization Advantages related to Database Organization? Security, etc. Disadvantages? Develop time, software, etc…

Some Terms… : 

DBA – tasks? Schema – description of the overall layout/structure used by the database software to maintain the db. Subschema – a piece required by specific users based upon needs – like what / why? DBMS? Some Terms…

Conceptual layers of a database : 

Conceptual layers of a database DBMS – heart of the system – but what do you get?Expensive?Players?Alternatives (ie, doing your own)?

Relational Database : 

Relational DB - There are different types of databases, but today – the relational is the most popular. Shows data in tables (like a spreadsheet) – these tables are in a sense relations. Relational Database

Relational Database : 

Relational Design: (process of setting up the necessary tables/relationships) – incorporates and uses such tools as ER Diagrams and Normalization. (you might try doing a Google search on ER Diagrams) GOAL of Design? (reduce problems associated with adding, changing, deleting data - ie - take care of any potential anomalies) Relational Database

A relation containing employee information (look ok???) : 

A relation containing employee information (look ok???)

A relation containing redundancy – look ok? : 

A relation containing redundancy – look ok?

An employee database consisting of three relations (continued) : 

An employee database consisting of three relations (continued)

An employee database consisting of three relations (continued – J O B) : 

An employee database consisting of three relations (continued – J O B) Now have Employee and Job – enough or do we need more? What might our ER-Diagram look like?

Finding the departments in which employee 23Y34 has worked : 

Finding the departments in which employee 23Y34 has worked

Finding the departments in which employee 23Y34 has worked : 

Finding the departments in which employee 23Y34 has worked

Additional Terms-for accessing data : 

Select – gets rows (tuples) from a table – while the Project extracts columns.Join – used to combine different relations into one.Example based upon SQL:Select Name, Phone from STUDENT Select Name, SSNum, GPA from STUDENT where Name = “Will E. Makit”Select Name, Major from STUDENT, COURSE where STUDENT.SID = COURSE.SID and COURSE.NUMBER = “CST123” Project Sel, Prj Join, Sel, Prj, Additional Terms-for accessing data

The SELECT operation : 

The SELECT operation

The PROJECT operation : 

The PROJECT operation

Figure 9.10: The JOIN operation : 

Figure 9.10: The JOIN operation

Using the JOIN operation : 

Using the JOIN operation So what would the join like here…. Write it?

Using the JOIN operation : 

Using the JOIN operation

Database… : 

OOD – databases based on objects that are linked to each other to show relationships Again, idea of having objects (including of course the data and methods) represent the data.Commit/Rollback – all about making sure that the data is correct, even in the event of a problem like malfunction, change of state, etc. Uses a log system to help control and monitor. Locking – helping coordinate problems associated with multi-user related activities.(Reading vs Writing needs) Database…

Social Impact of Databases : 

-- HUGE AREA -- Can now collect a ton of info on you – like what? But WHO owns the data Who can access it? (Parents, teachers, …) Can/should it be sold? (Harvard Prof – DMV, IRS, Credit Card, AOL, OIT, etc.) Privacy / Security / Laws Bottom Line – what do db’s help us with and what is becoming so crucial today? Future – and relationship to AI Social Impact of Databases

Slide 25: 

Review Next week: speaker on software performance Schema Layers of abstraction, data independence Relational models Relational operations - SELECT, PROJECT, JOIN instructions Converting above to SQL instructions Homework: Ch 9 page 397-399 # 10, 32.