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Database Design process and data description

1. Requirements analysis stage (accurate understanding and analysis of user requirements, including data and processing)

two。 Conceptual structure design phase (through the synthesis, induction and abstraction of user requirements to form an independent DBMS conceptual model)

3. Logical structure design phase (transforming the conceptual structure into a data model supported by a DBMS and optimizing it)

4. Database physical design phase (selecting a physical structure for the logical data model that is most suitable for the application environment (including storage structure and access methods))

5. Database implementation phase (designers use the data language, tools and host language provided by DBMS to establish the database, compile and debug applications, organize data storage and debug according to the results of logical design and physical design.

6. Database operation and maintenance phase (evaluate, adjust and modify the database system during operation)

Try to describe the design pattern formed by the structural design part in the process of database design.

The main contents are as follows: (1) the independent machine characteristics are formed in the conceptual design stage, which is independent of the conceptual model of each DBMS product.

(2) in the logical design stage, replace the Emurr diagram with the data model supported by the specific database product, such as the relational model, form the database logical schema, and then establish the necessary view on the basis of the basic table to form the external schema of the database.

(3) in the physical design stage, according to the characteristics and processing requirements of DBMS, the physical storage is arranged, the index is established, and the schema in the database is formed.

Characteristics of database design

(1) Database construction is the combination of hardware and software, and development (technical management and interface).

(2) from the perspective of software design, database design should be combined with application system design, that is to say, the whole design process should closely combine structure (data) design with behavior (processing) design.

What is the design goal of the requirements analysis phase? What is the content of the investigation?

Design goal: through a detailed survey of real-world processing objects (organizations, departments, doors, enterprises, etc.) to fully understand the working situation of the original system (manual system or computer system), and identify the various needs of users, and then determine the function of the new system again.

The content of the survey is data and processing, that is, the following requirements for the database:

(1) Information requirements, which means that users need to obtain the content and nature of information from the database. Information requirements can be used everywhere, that is, what data needs to be stored in the database.

(2) processing requirements, refers to what processing functions the user completes, what requirements are required for the corresponding processing time, and whether the processing mode is batch processing or online processing.

(3) Security and integrity requirements.

What is the content and function of the data dictionary?

(1) data items; (2) data structure; (3) data flow; (4) data storage; (5) processing process

Among them, data items are the smallest constituent units of data, and several data items can form a data structure. Data dictionaries describe the logical contents of data flow and data storage through the definition of data items and data structures.

The role of data dictionary: data dictionary is about the description of the database, in the requirements analysis stage, is the basis of the next step of conceptual design, and constantly modify, enrich and improve in the process of database design.

The conceptual structure of the database? Try to describe the characteristics and design strategy

Conceptual structure and conceptual model, the main characteristics are:

(1) it can truly reflect the real world, including the relationship between things and things, and can meet the data processing requirements of users, which is a real model of the real world.

(2) it is easy to understand, so that it can be used to exchange views with unfamiliar computer users. Active user participation is the key to the success of the design. (3) easy to change, when the application environment and application requirements change, it is easy to modify and expand the conceptual model.

(4) it is easy to transform to various data models such as relation, mesh, hierarchy and so on.

There are usually four kinds of conceptual structure design strategies.

(1) Top-down, that is, the global conceptual structure is defined first, and then refined step by step.

(2) from the bottom up, that is, we first define the conceptual structure of each local application, and then integrate them to get the global conceptual structure.

(3) gradually expand, first define the important core conceptual structure, and then expand it incorrectly, and gradually generate other conceptual structures by snowball method, up to the overall conceptual structure.

(4) the hybrid strategy, that is, the combination of bottom-up and top-down, uses the top-down strategy to design a framework of global conceptual structure.

The importance and Design steps of Database Conceptual structure Design

Importance: database conceptual design is the key to the whole database design. The application requirements obtained in the requirements analysis phase are first abstracted into conceptual structure and then used as the basis to implement other requirements.

Design steps: there are many design methods of conceptual structure design, of which the most commonly used method is bottom-up. The design steps of this method have two steps: 1 is to abstract data and design local views, and the second part is to integrate local views to get the global conceptual structure.

What is the Emurr diagram? What are the basic elements of the Emurr graph?

(1) the Emurr graph is an entity-relation graph, which provides the representation of entities, attributes and contact methods to describe the conceptual model of the display world.

(2) the attribute, represented by an oval, is connected to the application entity with an undirected edge.

(3) the type of contact, which is expressed in a diamond, with the contact name written in the diamond box and connected with the relevant entity with an undirected edge, and at the same time, the type of side-marked connection on the undirected edge (1)

What is the logical design of database?

(1) transform the conceptual structure into general relation, mesh and hierarchical model.

(2) transform the transformed relational, mesh and hierarchical model to the data model supported by specific DBMS.

(3) optimize the data model.

Rules for transforming Emurr diagrams into relational models

An entity is transformed into a relational model. The entity attribute is the relation attribute, and the entity code is the relation code.

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