What is the nested model of the set?

The

model of the nested set is also known as an algorithm for pre -ordering trees for pre -order and is a way of storing hierarchical data in relational databases. This model has the advantage of providing very fast access and is best implemented in hierarchies that are read more often than written. Each node within the information model is assigned two numbers that are stored as attributes. Inquirying the nested model of the set is relatively easy, because both values ​​can be used to pull out the necessary data. However, creating advertising, deletion, movements and updates is much more cumbersome because they may include nodal renumbering. The tree in this case is a data structure that contains a number of connected nodes. For example, a parent node can join several children's nodes and this structure is repeated through a tree via several levels.

Trees are a great way to store information in a certain order within a relational database, which is a set of data that stores data in the vertisnost on common characteristics. For example, product information in the food store in the shop can start with food, branching into fruits, vegetables and meat. Fruits can be further divided into berries, melons and apples and vegetables into tubers, green and more and meat into pork, mutton and veal.

The

relational database stores all this information in an easy -to -understand form and the nested model of the set allows you to effectively manage the tree structure. Using the above example, a root node would be a food that is represented by two values. Due to the left value for food like 1, the other items in the tree are assigned to the left OK. The fruit would gain 2 on the left, the berries would be 3 and so on. Value is then assigned to the right side, working all the way through the tree, bottom to top, each branch until the last value is assigned to the right side.

6 For example, if OVThe oce is 2 and 15, then all nodes that have left values ​​greater than 2 and the right values ​​less than 15 are the offspring of the fruit tree 2-15. It is easy to pull out information about all sheeps at the same time, because these values ​​can be entered in a single question in the database.

This model is excellent for storing information that is often accessible, but advertising, deletion and conversion of information into the model nested sets become very tiring. Rewriting indices and renumbering of information can cause the database to collapse, especially if the tree grows to hundreds of thousands of nodes. The model of the nested set is best for light content management systems that have minimal advertising and changes. Advertising can be nested much faster in the nested interval model because it stores the location of each node in a tree using decimal places with a movable point while encoding the path information.