Understanding the 7 Key Types in ER Diagrams
Before study about keys, first we want to know some basic things about ER diagram.
What is an Entity Relation(ER) diagram?
An Entity Relation(ER)is a form of flowchart that shows the relationships between “entities” like people, things, or concepts inside a system. ER Diagrams are most frequently used in the disciplines of software engineering, business information systems, education, and research to build or troubleshoot relational databases. They are also known as ERDs or ER Models, and they use an existing set of symbols to represent the interconnectivity of entities, connections, and their qualities. These symbols include rectangles, diamonds, ovals, and connecting lines. They have verbs for connections and nouns for entities, mirroring the grammatical framework. Data structure diagrams, which emphasize relationships between elements inside entities rather than interactions between things themselves, are connected to ER diagrams. ER diagrams also are often used in conjunction with data flow diagrams (DFDs), which map out the flow of information for processes or systems.
Components of Entity Relation diagrams:-
Entities: Within a database system, entities serve to represent actual physical objects, ideas, or things. They can be anything from persons and locations to items, orders, or transactions, and are often nouns. Entities are shown as rectangles in an ER diagram.
Attributes: Attributes are the characteristics or properties that describe the entities. They provide more detailed information about each entity. Attributes are represented as ovals connected to their respective entities.
Relationships: Relationships show how entities in a database are related to or associated with one another. One-to-one, one-to-many, or many-to-many relationships can be used to specify how data is shared and organized across entities. Relationships are shown as lines joining objects, with labels denoting their nature (such as “works for,” “owns,” or “is a part of”).
Purpose of ER Diagrams:-
They give stakeholders a clear visual depiction of the database structure, which makes it simpler to comprehend and explain the database architecture.
They assist in locating and fixing design flaws including omitted characteristics, superfluous data, or erroneous relationships.
They operate as a base for producing SQL code, database schemas, or data modelling tools to build the real database.
Keys in ER diagrams:-
A key is used in the definitions of various kinds of integrity constraints. A table in a database represents a collection of records or events for a particular relation. Now there can be thousands and thousands of such records, some of which may be duplicated.
super key: is a group of characteristics that may be used to specifically identify entries inside an entity. It could have more qualities than the bare minimum required for the main key or a candidate key. A superset of keys are called super keys.
Candidate Key: An property that identifies a row in a table in a unique way is a candidate key. One of the potential keys is chosen to be a table’s primary key. Therefore, candidate keys share the same characteristics as the main keys that were described before. A table may include several candidate keys.
For each table, there may be more candidate keys than one, but they may never be empty. Each candidate key has certain data and value. In addition to these traits, a combination of qualities also functions as a collection of potential keys.
Composite Key: A composite key is a key made up of two or more qualities that, when combined, provide each record in an entity its own unique identification. To show the composite key in the diagram, you would emphasize many properties.
primary key: If you’re wondering what is primary key in DBMS, primary key is a column of a table or a set of columns that helps to identify every record present in that table uniquely. There can be only one primary Key in a table. Also, the primary Key cannot have the same values repeating for any row. Every value of the primary key must be different with no repetitions. Amid many details, a primary key is the most significant one to understand what are keys and what is primary key in DBMS.
The PRIMARY KEY (PK) constraint put on a column or set of columns will not allow them to have any null values or any duplicates. One table can have only one primary key constraint. Any value in the primary key cannot be changed by any foreign keys (explained below) which refer to it.
Foreign Key (FK): A foreign key is an attribute or set of attributes in one entity that references the primary key of another entity. It establishes a relationship between two entities, ensuring referential integrity.
Alternate Key: An alternate key is a candidate key that is not selected as the primary key. In some cases, multiple candidate keys exist, and one is chosen as the primary key while the others become alternate keys.
Unique Key: Unique Key is a column or set of columns that uniquely identify each record in a table. All values will have to be unique in this Key. A unique Key differs from a primary key because it can have only one null value, whereas a primary Key cannot have any null values.
Among the seven types of keys available in the DBMS, a few other types of keys in SQL are also accessible. The key type is called Artificial Keys. An artificial has no relevance or meaning to the business but is often used to tackle conflicting data management situations. For example, if there is no attribute that comprises all required primary key properties or if the primary keys are complex.
