Melaniean Entity Is A Real-World Object Such As A Customer

Melaniean Entity Is A Real World Object Such As A Customer A Car

Melaniean Entity Is A Real World Object Such As A Customer A Car

(Melanie)An entity is a real-world object, such as a customer, a car, a class, or a student. (Coronel.) A relationship is an association between entities, identified with a verb: a customer buys a car and a student takes a class. Relationships between entities operate in both directions - a car is bought by a customer and a class is taken by many students. In a one-to-many relationship, the "one" is normally considered a parent entity, and the entity on the "many" side is usually considered the child or related entity. The strength of a relationship is based on how the primary keys of the related entities are defined. (Coronel.) Relationships are established by having the primary key of the parent entity included among the attributes of the child entity as a foreign key.

In a weak, non-identifying relationship, the primary key of the child entity does not contain a primary key component of the parent entity. On the other hand, in a strong, identifying relationship, the primary key of the related entity contains a primary key component of the parent entity. The strength of the relationship depends on whether the primary key of the child entity includes and thus identifies the primary key of the parent entity. In addition to relationships, entities can be strong or weak as well. A weak entity must meet two conditions: 1) the entity cannot exist without the parent entity and, 2) the entity has a primary key that is partially or totally derived from the parent entity in the relationship. (Coronel.) A loan cannot exist without a borrower and a dependent for a company insurance policy cannot exist without an employee.

Because a weak entity, by definition, must include a primary key component of the parent entity as part of its own primary key, a weak entity can never be in a weak relationship. Reference: Coronel, C., & Morris, S. (2019). Database systems: Design, implementation, and management (13th e). Cengage Learning. (Adam)When you are examining the strength of a relationship and how that factors the strength of entities, first you should define what makes a relationship or entity strong/weak. A weak entity is one that only exists when its parent entity exists.

An example of a weak entity would be a “CHILD” only exists if it has a “MOTHER”. Since children cannot be created in a lab yet, every child in existence has at least a biological mother that they were created by. A strong entity on the other hand is an entity that exhibits existence-independence, meaning it can stand on its own without a dependent entity. If you had a table in a database for people who had registered online for an email service, you may have a field title “REGISTRANT” where each entity is the person who signed up. They all signed up independently of each other and they don’t rely on any other aspect of the database.

They could share info with other tables, but they could also stand alone. Similarly, a weak relationship is one in which the primary key of a dependent entity does not contain the primary key of parent entity (Coronel & Morris, 2018). An example would be a “VEHICLE” entity that has its VIN as the primary key and a “SERVICE” entity that uses an incrementing number as its primary key. This wouldn’t be the best way to do it, but this would be a weak relationship. Conversely, a strong relationship is when the primary key of a dependent entity contains the primary key of parent entity.

To follow the example I laid out earlier, if the “SERVICE” entity was using the VIN of the vehicle in combination with the auto-incrementing number as the primary key, those two entities would be in a strong relationship. This means that a strong relationship is existence-dependent and a strong entity is existence-independent. My initial impression upon reading that was a case of puzzlement, but after a little bit of thinking it made sense. To be strong an entity shouldn’t be dependent on any other entities, whereas if a relationship is strong it should be dependent on the related entity. Reference: Coronel, C., & Morris, S. (2018).

Paper For Above instruction

The concepts of entities and relationships form fundamental building blocks in database design, shaping how data is stored, interconnected, and retrieved. An entity is a real-world object with distinct characteristics that can be represented within a database. As examples, entities such as customers, cars, students, or classes embody tangible or conceptual objects that are relevant to the domain being modeled. The importance of identifying entities accurately lies in ensuring data integrity, efficient storage, and meaningful associations that mirror real-world interactions.

Relationships define associations between two or more entities. These associations are often described using verbs or descriptive phrases, such as "buys" for a customer and a car, or "takes" for a student and a class. Relationships facilitate understanding how entities are related within the dataset, and they serve as the backbone for establishing meaningful connections in a relational database. Relationships may operate bidirectionally; for instance, a car is bought by a customer, and a customer may have purchased multiple cars, indicating a one-to-many relationship dynamic. Understanding whether a relationship is strong or weak is vital, as it influences how primary keys and foreign keys are structured.

A strong relationship, also called an identifying relationship, occurs when the primary key of the child or dependent entity includes the primary key of the parent entity. This means the existence of the dependent entity is contingent upon the parent entity, which aligns with the concept of existence dependency. For example, a "SERVICE" record that uses the vehicle's VIN combined with an auto-incremented number as its primary key exemplifies a strong relationship, where the service cannot exist without an associated vehicle. Conversely, a weak relationship, or non-identifying relationship, exists when the primary key of the dependent entity does not contain the primary key of the parent. An example would be a vehicle entity with VIN as its primary key and a service entity with a separate unique identifier, such as an auto-increment number, indicating independence.

Weak entities are fundamentally dependent on their parent entities for existence. They cannot exist without their parent and possess primary keys derived partially or wholly from the parent. A typical example is a "CHILD" entity that depends on a "MOTHER" entity; without a mother, the child’s existence is meaningless within the database context. On the other hand, strong entities can stand independently—such as a "REGISTRANT" in an online email registration database—who do not rely on other entities for their existence. This distinction underscores the importance of understanding entity strength in designing robust database schemas that accurately reflect domain requirements.

The decision to model relationships as strong or weak has significant implications for database normalization, referential integrity, and overall system robustness. Strong relationships enforce tighter coupling where dependent entities are meaningfully bound to their parent entities via primary keys, ensuring data consistency and integrity. Weak relationships, while more flexible, require careful handling to prevent orphaned records and maintain data coherence. Recognizing whether an entity is existence-independent or dependent helps database designers implement appropriate constraints and cascade operations, thereby improving database reliability.

In conclusion, understanding the nuances of entity strength and relationship type is essential for effective database design. Strong entities are autonomous and stand independently, whereas weak entities rely on parent entities for their existence, often reflected through primary key composition. Whether modeling a dependent "CHILD" or an independent "REGISTRANT," these principles guide schema development toward creating systems that are logically sound, maintainable, and aligned with real-world doings. Therefore, mastery of these concepts is crucial for database professionals aiming to develop efficient, accurate, and resilient data management solutions.

References

• Coronel, C., & Morris, S. (2019). Database systems: Design, implementation, and management (13th ed.). Cengage Learning.
• Coronel, C., & Morris, S. (2018). Database Principles: Fundamentals of Design, Implementation, and Management. Cengage.
• Elmasri, R., & Navathe, S. B. (2015). Fundamentals of Database Systems (7th ed.). Pearson.