Database Review ④

Database Review ④

June 15, 2016

21:34

Main Logical Data Model (LDM) logical

1. Three elements of the logical data model:

Data Structure data structure

Data Operation manipulation

Data Constraints constraints

2. History of the relational model

• E.f.codd, a researcher of IBM company, proposed relational model in 1970
• Proposed the Relational-algebra

Propose relational algebra

• Defined the 1st, 2nd, and 3rd Normal Forms of relational model in 197

Defining the first paradigm (1NF) in 1972, the second paradigm (2NF), and the third paradigm (3NF)

• Proposed BC NF in 1974

BC Paradigm presented in 1974 (BCNF)

3. relational database

became the mainstream of the database products after 1980s

relational database became mainstream database product in the 1980s

A typical relational database represents:

ORACLE, SQL Server, Access, DB2

4.ER model and Relational model

• is a model of the data.
• Er models have a lot of concepts

Entity entities, relationship relations, attribute attributes, etc.

Very good to meet the needs of the application

Not suitable for the needs of computer processing

• Relational model

There is only one concept: relationship relation

The physical world is made up of a collection of tables

Well enough to meet the needs of the computer for data processing

5.Database & Schema & Instance Databases & patterns & Instances

A student party, a simple analysis of the three concepts through other blogs and their own understanding.

　　The database , which is the database, consists of data and base, which literally means the warehouse where the data is stored. This understanding is justified. As to why there is a database, it is a matter of returning to people's handling of the data. At the very beginning, people in the computer industry who were able to process data needed professional knowledge, so the data was manually maintained, copied, and restored. Then in the development of storage media and the reduction of the threshold of the computer, the previous human management system has been unable to meet the needs of data management and processing, the next entry is the file system era. By a separate file for data storage, you can also understand that you own an electronic song, your classmates want a copy. Students can use a variety of storage media to copy one copy. But for an enterprise a company carcass, so the continuous copying of data, not only consumes a lot of storage space but also caused the data of different steps. There is a need to develop, the database facing the edge, through the storage of data and the connection between data, the use of optimized storage, not only to solve the data redundancy, and to deal with Big Data query update and other operations are also easy. More detailed explanations of the database can be found in my blog park related to the database blog: Eden Point-Blog Park

　　schema is a pattern , and when we talk about patterns on a database basis, we can understand the structure of data storage. Take an example: need to use some wood to make a cabinet, cabinets have many kinds of, can be a lot of drawers of the kind, can also be a drawer is divided into a lot of drawers, in addition to imagine some drawers are and other drawers in time and space is connected (this is really very powerful) Maybe this connection may be a lot of heavy (Chong ), one attached to the other. There are also many kinds of drawers, or in the direction of the drawer in different connected to the other drawer is not the same. corresponding to the database storage data structure can also be a relational database, chain database, mesh database and so on. As for the schema, when discussed with relation, it is probably possible to describe this: corresponds to the programming language concept of type definition. Cite an example of a program: String movie = "Spiderman". Here string is also the schema.

instance is an example , for the programmer to understand object-oriented programming, the example of this thing is really not strange. The simple one can be object obj = new Object (). Just kidding. Example: The program ape can not find the "object", the side of the small partners may say to him, construct a bar. The structure here is to write some classes by themselves (as for what is a class, you do not want to describe here, it can be understood as a processing plant, which abstract attributes and actions). Use these classes to construct your own "objects". can be initialized to "164cm" "C" Balabala ... That's the way it is. When it is linked to a pattern, it can be thought of as a record of some numeric values, such as relational databases, where the table's instance is a column of values in a relational database.

A student party, it is inevitable that there will be improper interpretation or wrong place also please forgive.

Database Review ④