First, Visual FoxPro Basics
1. Basic concept:
l Data: The physical symbol that is capable of identifying on a medium.
l Phase of computer data management development: manual management, file system, database system, distributed database system and object-oriented database system.
l Database management system DBMS (Database Management System): Software formulated, used, and maintenance for the database.
l Database: Store on a computer storage device, structured related data collection.
l Database Application System: System Developers use database system resources to facilitate application software systems for a certain type of practical application.
l The interrelationship between the various levels of software in the database system (from the inside):
1) Hardware
2) Operating system (database administrator)
3) Database management system (database administrator, developer)
4) Database application system (database administrator, end user)
l Database system: The computer system after the introduction of database technology, realizes organized, dynamically stored a large number of related data, providing a means of convenience of data processing and information resource sharing.
l The database system consists of hardware systems, database sets, database management software, and related software, database administrators, and users.
l The characteristics of the database system:
1) Realize data sharing, reduce data redundancy
2) Adopt specific data model
3) Has high data independence
4) Have a unified data control function
L (Class): Description of a class of object properties, these objects have the same properties: the same type of properties and methods.
l Object: Package consisting of properties and related methods.
l Attribute: Represents the status of the object.
l Method: The process of describing object behavior.
l Instance: A variety of generated objects are called instances of this class.
l Event: Action is pre-defined by the system and is made by the user or system.
2, relational database
l Entity: objectively exist and can distinguishably different from each other.
l The properties of the entity: describe the characteristics of the entity.
l Substantimetric: The set of attribute values represents an entity, and a collection of attributes represents a type of entity called a physical type.
l Entity set: Collection of the same type of entity.
l One-to-one relationship: In the VFP, it is manifested as a record in the primary table.
l One-to-many relationship: In the VFP, it is manifested as a plurality of records that are recorded in the related table in the VFP.
l Multi-to-Many RelationShip: In the VFP, it behaves as multiple records in a table, there are also multiple records in the related table.
l Data model: Database management system is used to represent a method of contact between entities and entities.
l Hierarchy Model: The model represents the entity and its model between the tree structure. Features: There is only one parent node for each node, there is only one node without a father node.
l Mesh model: Model between the entity and its connection with the mesh structure. Features: Each node can have multiple parent nodes, and there are multiple nodes without a parent node. 1) Relationship database
i. Relationship model: Use two-dimensional table structure to represent the model between the entity and the entity.
II. Essential differences from hierarchy models and mesh models: Data description consistency, model concept.
Iii. Relationship: A relationship is a two-dimensional table, each relationship has a relationship name.
IV. Relationship mode: Description of the relationship.
v. Relational structure: a relational mode corresponds to a relational structure. Format is: Relationn Name (Attribute Name 1, Attribute Name 2, ..., Attribute Name N) In VFP: Table Name (Field Name 1, Field Name 2, ..., Field Name N)
VI. 元 元: In a two-dimensional table (a specific relationship), the line in the horizontal direction becomes a tuple, and each line is a tuple.
VII. Properties: Columns in the vertical direction in the two-dimensional table, each column has a attribute name.
VIII. Domain: The range of value of the property, that is, the range defined by the different tabs to the same attribute.
IX. Keywords: The combination of attributes or properties, its value is the only standard is a tuple. In VFP, the only standard labeled label is a tuple.
x. External Keyword: If a field in the table is not the primary keyword or candidate keyword in this table, it is the primary keyword or candidate keyword for another table. Then this field (attribute) is called an external keyword.
Xi. Characteristics of Relationship
1. The relationship must be standardized.
2. The same attribute name cannot appear in the same relationship.
3. The exact identical tuple is not allowed in the relationship.
4. Nothing in the order of a relationship between the ingredients.
5. Nothing in the order in a relationship.
2) Relationship operation
i. Select: From the relationship to find the operation of the tuples that meet the conditions, the result is a new relationship.
Ii. Projection: Develop a new relationship between several attributes in relationification mode.
III. Joint: Two relational patterns spliced into a wider relationship mode.
3) Consistency and integrity of data
i. Entity Integrity: To ensure that the unique features in the table, that is, repeated records are not allowed in one table. In VFP, the primary keyword and candidate key are implemented.
II. Domain Integrity: Limited the content, type, and value range of fields.
III. Reference Integrity: When the data is inserted, deleted, or modified in a table, check whether the data operation of the table is correct by applying data in another table associated with each other.
