1. The four basic concepts
(1) Data
Foreign name : Data
Official definition : Symbol record describes things
Weird and incomprehensible : a variety of graphics, text, numbers, and even audio and video data are also self-expression that is considered something of things. (Having said that, or people define good)
(2) Database
Foreign name : Database, referred to as DB
Official definition : The database is long-term storage in the computer, organized , and can share the large amount of aggregate data.
Weird and incomprehensible :
1. Database, all libraries, and certainly a lot of data collection;
2. the organization so much data is sure to have certain rules (ie organized), or the more the more chaotic, there is no question which people want more to the more complex;
(! benefit of the people) 3. so time-consuming to set up a database only for themselves, and that's not worth it, so it must be shared
4. in addition, long-term storage, if I take the trouble to build the database, to be gone a few months, then I certainly did when establishing power, slowly it will lose my mind! It is not a program you want to lose popular support! Moreover, since it is to be shared, of course, can not easily disappear. .
(3) database management system
Foreign name : DBMS
Official definition : it is the basic software, is a large and complex software systems, data management software layer located between the user and the operating system.
Weird and incomprehensible : As the name suggests, is a drop in our database management software, called "System", and similar operating system is the foundation software. We want to use SQL Server, My SQL, and so is its friends.
(4) database system
Foreign name : DBS
Official definition : by the database, data management systems, applications, database administrators whole constituted.
Weird and incomprehensible :
look at the name, so abstract, highly summarized, certainly including many. . . Like a small company, the company needs to operate, require basic financial capacity (database), the management system (DBMS), personnel management (database administrator), there is the company's achievement (developed applications).
2. A conceptual model of four concepts
(1) entity
Foreign name : Entity
Official definition : the objective existence of things can be distinguished from each other.
Weird and incomprehensible : specific person, and things, as well as some abstract concept that we recognized, (similar to a professional like this).
(2) an entity type
洋名：Entity Type
Official definition : The entity name, attribute name and describe the same set of abstract entity becomes an entity type.
Weird and incomprehensible : "type", that is abstract, that is, the same type of entity extraction common property, but no specific value, the entity is an entity type for.
For chestnut : Student (Student ID, name, sex, age, professional ...)
(3) entity set
Foreign name : Entity Set
Official definition : a collection of the same type of entity.
Weird and incomprehensible : I think the definition has been very easy to understand it. Let students on entities, it is the student's entity set 1 (), 2 students (), ... students n (), () which is their own property.
(4) the links between entities
洋名：Relationship
Official definition : the link between internal things and things in the real world reflected the link between internal and entities associated with entities in the information world.
Weird and incomprehensible :
It reflects things as an entity that links between entities, is our reality in the connections between things.
Students and teachers entity like entity, whether in the real world or the world of information, after all, he is your teacher.
3. The relational model concepts
(1) relational model
洋名：Relational Model
Official explanation : in the user's point of view, the logical structure of data in the relational model is a two-dimensional table, which consists of rows and columns.
Weird and incomprehensible : the relational model the user sees on the performance of a two-dimensional table, but it's definitely not a table so simple!
(2) the relationship - Table
Foreign name : Relation
Official definition : a relationship usually corresponds to what we call a table.
(Here is not weird and incomprehensible ....)
(3) Properties - Column
Foreign name : Attribute
Official definition : a table that is an attribute to each attribute a name, called the attribute name.
(4) field in the range of attributes -
Foreign name : Domain
Official definition : is a collection of values having the same data type. The range of attributes from a domain.
Weird and incomprehensible : As is often said mathematical function of our domain and range. Domain is a group of the same set of data types, the range attribute domain have significance.
(5) tuple - OK
Foreign name : Tuple
Official definition : a behavior table a tuple
(6) Code - tuple uniquely identified set of attributes
Foreign name : Key
Official definition : also known as code keys. Table a property group, you can uniquely identify a tuple.
Weird and incomprehensible : As our lives barcode, two-dimensional code. Each application is different code for each commodity, they were able to distinguish them. So the code is used to distinguish and uniquely identifies.
(7) component overlaps with a row of -
Official definition : a tuple attribute value.
Weird and incomprehensible : component of relations (tables) the smallest unit, the table is what we see in a grid - a row with an overlap.
(8) Relationship Model - Header
Official definition : is a description of the relationship.
Weird and incomprehensible : table relationship is the relationship model to describe the relationship, it is the header. Model is abstract and does not involve a specific value.
Three modes of the structure and its advantages 4.DBS
(1) three mode configuration
Three modes by the outer mode, mode, the mode configuration mode with the mode in which only one, there may be a plurality of outer pattern, may correspond to a plurality of applications on the basis of each of the outer mode.
(2) Mode
Foreign name : Schema
Official : also known as logical schema. It is a database of all description data logical structure and features. It is a common view of all data users.
Weird and incomprehensible : mode, that is, structural features of the data description, no other qualifier, will represent all data. . . (Myself feel a little far-fetched, but still confidently played out !!)
(3) Mode
Foreign name : External Schema
Official : also known as sub-mode or user mode. The user's local description of the logical structure and characteristics of the data. User database view, is a logical representation of data related to a certain application.
Weird and incomprehensible :
External mode, the external application near distance, near distance of the user, so the user is viewing angle, designed to apply to the user's needs, the use does not involve all the data, only part of the different needs, the data is also used it is different, it is possible to have a plurality of external modes.
It Hinako mode, by definition is part of the pattern, like a subset of the complete works relations.
(4) Mode
Foreign name : Internal Schema
Official : also called storage mode. Structure description data and the physical storage of the data in the internal database representation.
Weird and incomprehensible : in the mode, including, also known as storage mode, as the name suggests, refers to describe the data in the internal storage.
Advantages (5) three modes of the structure
To ensure the security of the database, each user can only see data and external access mode corresponding to the remaining data is transparent to the user, can not see, it can not change, ensuring the security of data.
5. Data independence and DBS poles image
(1) physical independence
Official : refers to the user's application and the physical storage of the data in the database are independent of each other.
Weird and incomprehensible : physical independence, by definition, independent of physical storage, changing the physical storage, applications do not need to change, that the application does not depend on physical storage is physically independent.
(2) Logical independence
Official : means a logical structure of the application and the user data in the database are independent of each other.
Weird and incomprehensible : to change the logical structure of the data, do not modify the application, that application does not depend on the logical structure of the data, the logic is independent.
(3) DBS two-stage image
Database system for physical and logical independently by two separate images.
1. Mode outer / mode map - logical independence
Mode is changed, by changing the external mode / map mode - ensure the external mode without modification, the application need not be amended.
ps: the logical schema is a description of the structure and features, mode change refers to a logical structure changed.
2. Mode / the mode map - physical independence
Physical storage structure changed, by changing the mode / mode within the image - the same assurance model, the application will not be affected.
6. A data definition language and data manipulation language
ps: there is no specific study, the following section for by Baidu.
(1) Data Definition Language (DDL)
It defines the database structure and method of operation and the like. For example, create and delete tables, indexes, and so defined. (Used to create, modify, and delete database tables, etc.)
(2) Data Manipulation Language (DML)
Basic manipulation of data, "CRUD."
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