Bio-based plastics HS code classification

List of contents of this article:

• 1,Bio-based plastics HS code classification In the database system, what is the data model realized by considering the data?
• 2, What commonly used data structures are used in the implementation of the database system
• 3, database transaction atomicity, how consistency is achieved< /Li>
• 4, Briefly describe the establishment process of a database application system

In the database system, what is the data model that considers the realization of data?

1. The multimedia data model mainly adopts the expansion of relational data model and the object-oriented design method. Because it is difficult to describe multimedia information and define the operation of multimedia data objects with traditional relational models, in addition to introducing abstract data types, the method of semantic models is more commonly adopted in relational model expansion.

2. Hierarchical model Hierarchical model is the earliest model used in the database system. Its data structure Q is a directed tree. The root node is at the top, the level is the highest, and the sub-knot is at the bottom, arranged layer by layer. The characteristics of the hierarchical model are: there is only one root node; other nodes have only one parent node mesh model.

3. Hierarchical modelType Hierarchical model is a tree structure model that organizes data according to natural hierarchical relationships to reflect the affiliation between data. Hierarchical model is the earliest developed and technically mature data model in database technology.

4. At present, most database management systems adopt relational data models. The relational data model is the cornerstone of the modern database management system. E.F., a researcher at IBM since the 1970s. Since Codd proposed the relational model, it has become a standard method for data storage and retrieval.

5. The data model corresponding to the tree diagram is a hierarchical model; the data model corresponding to the mesh diagram is a mesh model. The relational model is a non-formatted structure, which uses a single two-dimensional table structure to represent the connection between entities and entities.A two-dimensional table that meets certain conditions is called a relationship (see relational database).

6. Parametric and non-parametric models The models described by algebraic equations, differential equations, differential equations and transfer functions are all parametric models. Establishing a parameter model is to determine the parameters in the known model structure. The parametric model is always obtained through theoretical analysis.

What commonly used data structures are used in the implementation of the database system

Relational structure, also known as "relational model", refers to the number of entities in the form of a two-dimensional table to represent the connection between entities. According to the model. In the process of data development, three basic data models have been produced, which are hierarchical models, mesh models and relational models. These three models are named according to their data structure. The first two adopt formatted structures.

Single data structure-relationship (table file). The table of the relational database uses a two-dimensional table to store data. It is a logical group with relevant information arranged in rows and columns, which is similar to the Excle worksheet. A database can contain any number of data tables.

Array is the simplest and most common data structure. Their characteristics are that elements can be easily accessed through index (location). What are they used for? Imagine a row of theater chairs. Each chair is assigned a seat (from left to right), so each audience will be assigned a number from the chair he is going to sit on.

In a relational database, each relationship is a two-dimensional table. Both the entity itself and the connection between entities are represented by a two-dimensional table called "relationship", so that the data describing the entity itself can naturally reflect the connection between them.

Realize data sharing. Data sharing includes that all users can access the data in the database at the same time, and also includes users can use the database through the interface in various ways and provide data sharing.(2) Reduce the redundancy of data.

Database transaction atomicity, how to achieve consistency

1, the answer, he correctly pointed out that in order to ensure the atomicity of transaction operations, log-based REDO/U must be implemented NDO mechanism. But this answer is still incomplete, because atomicity cannot fully guarantee consistency.

2. Atomic transactions are the logical working units of the database. Each operation contained in the transaction is either done or not done at all. 2. The result of consistency transaction execution must be to change the database from one consistency state to another consistency state.

3. Atomicity means that the transaction is an inseparable working unit, and all the operations in the transaction are either successful or all failed.For example, SQL statements in the same transaction can either be executed successfully or failed.

Briefly describe the establishment process of a database application system

1. The content should include: system positioning and its functions, data resources and data processing capacity, human resources allocation, equipment configuration scheme, development Cost estimate, development progress plan, etc. After the feasibility analysis report and the database application system plan are approved and established, they become the outline of the follow-up development work.

2. Basic steps of database design: system requirements analysis and design. Conceptual structure analysis and design. Logical structure analysis and design. Physical structure analysis and design. System implementation. System maintenance.

3. The development of database application system is a software project.Generally, it can be divided into the following stages: planning. Demand analysis. Concept model design. Logical design. Physical design. Programming and debugging. Operation and maintenance.

4. Database physical design is to select a physical structure that is most suitable for the application environment for the logical data model, including storage structure and access method.