database

relational database

designed to fix problems from flat file and hierarchical databases -idea was developed by Edward F Codd an IBM in 1970

disadvantages of FFD

difficult to query difficult to compare data data can be redundant or inconsistant

advantages and disadvantages of Hierarchical DB

-AD:easy to navigate and process -DIS:Data Redundancy Difficult to compare data between branches

flat file database

-The simplest electronic database -structures are flat file structure. -Delimited -Fixed length -In a spreadsheet application

Relational Database Management Systems (RDMS)

-software that manages relational databases. -It must allow for the creation and maintenance of databases. -It usually has tools for backup and restoring databases. -It usually has tools for securing access to database objects. -It may have many other administrative and reporting tools.

chapter 1

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nature of relational DB

1.All data, even data about data such as a table and column names, are stored in tables. 2.Each row in a table should have a column (or columns) that uniquely identifies it, a primary key. 3. this primary key is repeated in other tables to create a relationship. 4.When it is repeated it is known as a foreign key.

SQL

Codd said that a relational database should have a sublanguage that can manage all data manipulations as well as DBMS processes such as security and backup.

delimited definition

Delimited : each piece of data is seperated from the next piece by a delimiter which is often a comma or tab. there are no tables. Fixed length

definition of database

a set of related data

hierarchical database

organized in a tree-like structure -every parent can have many kids but kids can only have one parent