A logical data structure or logical data model is defined as the high-level model of an operating data of the system. The relationships of the systems which they share are also a part of the logical data model. We will begin here discussing the modelling part.
Logical data structuring is the data modelling and is based on the identification of the aspects. The list includes the entities, their attributes, and the relationships of the entities. The system has to be modelled.
An entity is anything about which the knowledge has to be maintained in an enterprise. This can either be physical, or conceptual. An entity is something which a company has to keep the data off. Under the physical trait, we have an employer, a part of a machine and the machine itself is the physical aspect of an entity.
Whereas, in the conceptual concept we have a project, an order and a course.
An attribute is a feature of an entity. That characteristic of the entity is fully functionally dependent on it. The details of interest can vary from, for example, age, salary and goes to project leader, start-date and cost.
In the logical data structures, the entity types include the entities and the types of objects.
We can also term the entity types as the presentation of the information of the person, place, thing, event, purchase order, retail transaction. The list is extensive. They are included to describe the group or the set of a particular type, a game of entity for the occurrences and the instances purpose.
For example, the student is a set of students- any individual student is an entity occurrence. Also, it is an instance of the student entity type.
How to identify an entity?
Identifying the owner of a set of attributes becomes easy by knowing the fact that each instance of an entity varies from all others. Either one or more primary key qualities are unique to a particular case.
For example, a student has a student number; a project has a project code.
Read a table and examine yourself. Ask yourself whether you can identify the entities. Do the entities of the table have the attributes used to refer the other entities? You can also judge your information by thinking of the uniquely identifying characteristic.
Now, let us talk about the relationships between the entities and the attributes.
The names get identified,and the association of the two entity types gets defined with the help of relationships. There is a relationship between only two entity types. The number can’t be changed. Under the logical data model, verb phrases are used to represent the relationships. The two entities in the model can establish the relationship from either side between two entities. The two entity types bounded by the relationships have two roles to play:
1. One of the two would be the parent entity
2. Second would behave like a child entity
The child gets its entity from the parent which it shares with it. The dependent entity type comes to picture when the child entity inherits the primary key of the parent entity. A foreign key is the name of the attribute which they share.
Type of the data representation in the named format is called domain. The field applies to more than one attributes. We need to distinguish between them by defining the data type. These include integer, string, date, time, floating point, another standardized data type. It can be another definition in the extended format which assigns the custom properties to a base data type.
Entity and relationships
There are various types of relationships, and they are one to one, one to many and many to many relationships. Let us discuss them one by one in brief-
One to many relationships
Here, we mean by the one many relationships in the form that one record in a table called student may be related to some records in a subjects table. I will make it easy for you. A record in the subjects table can only be described to one record in the student'stable. We use the keys to mark the relationships between the two.
One to one relationships
This type of relations shows that there is a 1:1 ratio of the entity and the relationships. An entity becomes an attribute of the other. That is why it is called a one to one relationship. Over time includes more than one entity and relationship. 1: many connections.
For instance, there can be many managers of a factory. Also, he can be the manager of more than one factory in his career. This shows the one to one relationship between the manager and the factory. Keeping track of the need for the managing changes need an analyst. The manager will act as one of the attributes of the entity, factory.
Many to many relationships
In the M: N type of the relationship, a link entity is needed. There are attributes of every entity in the link entity. The two parameters which act as qualifiers are the time and the quality.
There are some components of the factory. For example, all the factories have the elements of the repair shops. Every component of the factory is repaired by one factory only.
These were about the relationships. Let us look at the questions related to them.
1. Which is not a logical database structure from the tree, relational, chain, network?
2. Which normal form is considered adequate for normal relational database design?
3. The distinguishable parts of a record are called from files, data, formats, fields?
4. Which of the following is the logical structure of one too many relationships?
5. The data dictionary is a special file that contains which of the following?
a) the names of all fields in all files
b) the data types of all fields of all files
c) Both of above
d) None of above
6. Administrative supervision of database activities is the responsibility of
a) Database administrator
b) DP Manager
c) DB Manager
d) None of above
7. Which of the following name does not relate to stacks?
a) FIFO lists
b) LIFO list
d) Push-down lists
8. In C how many parameters can passed to a function
d) as many as defined in the function definition
Try to answer these questions. If needed, search it over the internet. If you need, reread the article, follow the concept again.
All the best!