Since the development of database technology, there are mainly three data models: hierarchical data model, network data model, and relational data model. These three models are named according to their data structures.
Hierarchical model
It organizes data into a one-to-many relationship structure, and the hierarchical structure uses keywords to access each part of each level. The advantages are convenient and fast access; the structure is clear and easy to understand; data modification and database expansion are easy to implement; and it is very convenient to retrieve key attributes. The disadvantages are rigid structure and lack of flexibility; the same attribute data needs to be stored multiple times, and data redundancy is large (such as common edges); it is not suitable for the organization of topological space data.
Network model
It uses connection instructions or pointers to determine the explicit connection relationship between data, and is a many-to-many type of data organization. The advantage is that it can express complex relationships between data clearly and conveniently; data redundancy is small. The disadvantages are that the complexity of the network structure increases the difficulty of user query and positioning; it is necessary to store pointers of connections between data, which increases the amount of data; and it is inconvenient to modify the data (the pointers must be modified).
Relational model
It organizes data in the form of record groups or data tables to facilitate storage and transformation using the relationships between various geographical entities and attributes, without hierarchies or pointers. , is a very effective data organization method to establish the relationship between spatial data and attribute data. The advantage is that the structure is particularly flexible, the concept is single, and it meets the query requirements formed by all Boolean logical operations and mathematical operation rules; it can search, combine and compare different types of data; it is very convenient to add and delete data; it has higher data independence and more Good security confidentiality. The disadvantage is that when the database is large, it is time-consuming to find data that satisfies a specific relationship; spatial relationships cannot be satisfied.
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