Entity Relationship (ER) Model

The entity-relationship (ER) data model is created out of the activity of utilizing commercially accessible DBMS to model application database. Prior, business systems depended on the various leveled and network approach. The entity-relationship model is a speculation of these models. It contains an ER Diagram which is crucial for the overall ease and speculation on the ER Model.

Browse more Topics Under Structuring Database For Accounting

• Data Processing Cycle and Database for Accounting
• Designing Relational Database Schema and Interaction with Databases
• Entity Relationship (ER) Model
• Relational Databases and Schemas
• Illustration of Accounting Database

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ER Model and ER Diagram

ER Model permits the portrayal of explicit limitations and relationships. This model of the database comprises of entities, attributes, identifiers and relationship which are a way to express a reality for which database is to be made. The database structure, utilizing the ER Model, is typically demonstrated pictorially by the means of entity-relationship, i.e. ER diagram.

The entities and the relationships between them are demonstrated by using the ER symbols (part of ER diagram) to show various kinds of entities, attributes, identifiers, and relationships. The symbols, which are utilized for the purpose of an ER diagram, are institutionalized and are as per the following

ER Diagram

Entity Type as Rectangular Box

Weak entity Type as double lined Rectangular Box

Relationship Type as diamond-shaped Box

Identifying relationship Type as double
lined diamond shaped Box

Attribute names enclosed in ovals and
attached to their entity type by straight lines.

Key attribute names enclosed in ovals and
attached to their entity type by straight lines.

Multi-valued attributes by double ovals

Derived attributes by dashed line Ovals

Total participation of E2 in R

Cardinality Ratio 1 : N
for E1 : E2 in R

                                                 What is Relational Database Schema?? Learn here. 

Entity

Entities are the fundamental units utilized in modeling classes of concrete or conceptual objects. An entity is an object that is important to a business. Objects of the same kinds are described by a similar arrangement of attributes or properties. As such, we can state that the autonomous presence of a thing is known as an entity.

Most importantly, two objects are commonly recognizable and this fact is demonstrated in the entity set by giving them exceptional identifiers. In this way, an entity implies an object having a physical presence (e.g., individual, office, furniture, and so forth.) or conceptual presence (e.g., organization).

We have examined the accounting reality above. It has five entities – accounts, vouchers, employees, account types, and proof or support reports. In other words, the accounting information is collected through these entities.

                                              Learn about Data processing cycle and Database of Accounting here. 

Attributes and Identifiers

The properties that portray or further depict an element are called its traits. Each question must be independently recognized as a substance. Recognizing and ordering the items into an element can be troublesome in light of the fact that a question can have a place with various substances in the meantime or at least two elements might be comparative.

In such cases, they should be additionally depicted so every element is recognized and independently distinguished. Substances are recognized and displayed utilizing their qualities or properties.

An affiliation exists between various qualities of an element. A relationship between two properties demonstrates that the estimations of the related characteristics are associated. This correspondence between qualities of a substance is a property of the data that is utilized in displaying the question. Therefore, we recognize the affiliations that exist among the traits of a substance, called a relationship.

Think about the representatives of the firm. The firm keeps up certain data, for example, name, date of birth, address, assignment, name, and relationship of wards, about every representative. In any case, this data can coordinate with the data of some other representative. Along these lines, one of a kind data like worker distinguishing proof number or code is fundamental about every one of them by which they can be recognized. This one of a kind number is known as an identifier.

Entity Types and Entity Sets

(i) Composite versus Basic (or atomic) Attributes

The composite attributes can be diversified into sub-parts to speak to demonstrate some more basic attributes with free implications. The straightforward traits can’t be additionally sub-partitioned. For instance, Name of a man that is regularly subdivided into First Name, Middle Name, and Last Name is a composite trait. The tallness of a man is a straightforward quality as it is without further sub-division.

(ii) Single-esteemed versus Multi-esteemed Attributes

A trait with a solitary esteem for an element is single-esteemed rather than those which various qualities. For instance, the stature of a man is single-esteemed quality while the capabilities of that individual area multi-esteemed property.

(iii) Stored versus Determined Attributes

At least two properties might be connected in such a route, to the point that at least one winds up essential while alternate moves toward becoming reliant on that essential property. For instance, the date of birth of a man is a putaway property while the age of that individual is inferred quality.

(iv) Null Values

The absence of an information thing is spoken to by an extraordinary esteem called the invalid esteem. There are three circumstances which may require the utilization of invalid qualities

• When a specific ascribe does not have any significant bearing to a substance;
• Value of a quality is obscure, in spite of the fact that it exists;
• Unknown since it doesn’t exist.

(v) Complex Attributes

The composite and multi-esteemed qualities might be settled (or assembled) to constitute complex ones. The enclosure () is utilized for demonstrating a gathering of segments of composite qualities. The props {} are utilized for demonstrating the multi-esteemed qualities.

Relationships

A connection among elements is known as a relationship. The relationship set is utilized in the information displaying to speak to a relationship between element sets. This affiliation may have certain properties spoken to by the traits of the relationship set. A gathering of connections of a similar kind is known as a relationship set.

A relationship that includes N substances is called N-ary relationship. A relationship is a paired relationship if the number of entities sets engaged with the relationship is two. Enrolment is a case of a parallel relationship including two particular substance sets like between the understudy and course.

The examination is a case of a twofold relationship which demonstrates the connection between an understudy and move number. Similarly, processing is a case of a ternary relationship which speaks to the relationship including an understudy utilizing a specific figuring framework to do the calculations for a given course.

Similarly, at whatever point a characteristic charge or credit of one element compose voucher alludes to another element compose Accounts, there exists a connection between these substances as vouchers and Accounts. Vouchers and records are connected in two different ways, Vouchers contain the charge and furthermore the credit accounts. A relationship compose characterizes the relationship of substance compose and a relationship occasion is a relationship of element examples.

The sections of a connection hold the estimation of the credits that we wish to connect with every substance case, and each is marked with a particular property name at the highest point of the segment. This name, obviously, gives a remarkable reflection to the whole section or to a specific estimation of a tuple in the connection.

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Solved Question for You

Q: What is a weak entity?

Ans: A weak entity is one which does not have an identifier of its own. A weak entity type is identified with respect to its relationship because it cannot be identified without own owner entity. Let us consider a voucher.

A voucher may be accompanied by a set of support documents, such as bills, detail of expenses, issued by other parties to the transaction. Such support documents are weak entity type which is used to keep track of support documents attached to each voucher via N- relationship.