6) Give information about database (VB) models based on their structure.
The basis of the database structure is the concept of a data model.
A set of concepts, structures, and operations used to organize data at a logical
level is called a data model.
A data model is a set of concepts that describe the structure of a database. Or
we can say this, the data model (VM) determines how and with what rules they
are structured. It should be adapted to the selected model in the operations
performed on the data.
Database model; consists of data types, operations and data constraints.
There are different structural models of a database:
 Hierarchical
 Network
 Relation
 Object oriented
Multidimensional, post-correlation models can also be attributed to the new
models that have emerged in recent years and are applied in practice .
Hierarchical model is the first model used for database. It was widely used
in the 1960s and 1970s. This type of database is used by software running in the
host environment.
The hierarchical model is based on the representation of data in the form
of a graph (or tree) (Figure 1). In a schema graph diagram, vertices (nodes)
represent the type of entity, and branches represent the relationships between
entities. Often, this model is also called a branching (tree-like) model.
Hierarchical model - has a tree-like structure . The best example of using a
hierarchical data model is a family tree. Data has a parent-child relationship. Each
datum can have multiple children, only one parent. In this case, if the parent record
needs to be deleted, the child records are also deleted. The positive aspect of this
structure is that the search is fast, and the negative aspect is that it is difficult to
delete data from the structure.
In this model, data is represented by levels: a lower level and an upper level. The
lower level is subordinated to the upper level. In the hierarchical model, the design
is performed on the "top-down" principle. The main disadvantage of this model
is the unidirectionality of the relationship between the data, as well as the rigidity
of its structure, which means that adding or removing subtrees from the tree can
cause big problems. The following relationships are possible in a hierarchical
database: "one-to-one" (1:1), "one-to-many" (1:M).
Any node within the model can be connected to only one node above it
while connecting to n number of nodes below it. The node at the top of the
hierarchical structure is called the root.
A network data model is the most general data model among data models. In
VB's network model, data is accessed through paths, and one data can be accessed
in several ways. At this time, each data is actually related to several data, and the
relationships between them may not be hierarchical .
Network-type models are also based on data representation, just like
hierarchical models. An element in a network can be connected to any other
element. A network database can consist of several trees. Network databases store
data in the form of graphs, which are a more advanced form of trees.
The network model is considered a limited data model because multiple
connections cannot be established between nodes.
A network model is similar to a hierarchical model. Unlike hierarchical
structures, network structures have no restrictions in terms of connectivity.
Complexity and high cost are the main disadvantages of this model.
Due to the inadequacy of hierarchical databases, it is a type of database that was
created as a result of the joint work of scientists.
Unlike the hierarchical model, the network model implements (1:1), (1:M),
(M:N) functional relationships as well as many-to-one (M:1) relationships.
(Figure 2).
of the relational model and general relational model VBIS is connected
with the name of the IBM employee Edgar Kodd. The mathematician developed
the principles of this model based on set theory.
These principles generally consist of the following.
- Data is an ordered collection of rows called relations (tables):
- Rows differ from each other by the value of at least one field:
- Operations are performed entirely on a relationship, resulting in a
relationship
It is a data model that has been in use since the late 1970s and has been around
since 1985. The relational model is the most commonly used database model
today
The central object of VB is a table. Today, VB based on a table is more
common. The simplest VB has at least one table. In general, VB usually
has dozens of tables.
The basis of this model is the mathematical concept of "ratio". Subject to
certain conditions, the ratio can be described as a two-dimensional table that is
common to humans. The vast majority of DBMS available for personal computers
use the relational model.
The advantages of the relational model are as follows:
 simplicity
 ease of program implementation
 the possibility of performing various mathematical and logical operations
on the data
 the possibility of building a flexible VB scheme that provides an answer
to any type of request.
Relational data model
reflects the relationships and the relationships between them that cover the
subject area . In this model, the logical scheme of VB is described in the form of
a ratio scheme. In that scheme, separate ratios and the relationships between them
are indicated by the axis lines. Each row of the table consists of fields with the
same structure. Relatively, a row of a table is called a tuple, and a column is called
a domain. A named domain is called an attribute. The strength of the ratio is
expressed by the number of tuples, and the power by the number of domains
(columns).
The object-oriented model combines two models - relational and network
models - and is used to build large VBs with complex structures. The principles
of object-oriented programming are used in the object-oriented model. But here,
users do not work with hardware and software concepts (bytes, writes, etc.), but
with concepts corresponding to the structure of the real world, in other words,
with objects and the operations assigned to them. The structure of object-oriented
VB can be graphically described in the form of a tree whose vertices are objects.
The properties of objects are described by any standard type (for example, String)
or by the type defined by the user as "class".
Object-oriented VB search consists of determining the similarity between
the object specified by the user in the query and the object stored in VB.
The object specified by the user and called "goal" (its property is defined
by the "goal" type) can generally be a subset of the entire hierarchy of
objects stored in VB. The object-goal and the result of the request can be
stored in VB itself. The advantage of the object-oriented data model
compared to the relational model is the ability to reflect information about
the complex relationships of objects. The object-oriented model allows
defining individual VB scripts and their processing functions. The
disadvantage of the object-oriented model is its complexity, inconvenient
data processing and low query execution speed.