![Data Model Elements 10
ER models have the following core concepts
Entity – A concept to abstractly represent all instances of a group of
similar ‘things.
An entity is a class of persons, places, objects, events, or concepts
about which we need to capture and store data.
An entity instance is a single occurrence of an entity.
Attribute – a descriptive property or characteristic of an entity. It is
a simple, atomic data item like a date, a name, a number [also called
Property or Field ]](https://image.slidesharecdn.com/aakankshasonik-150415053206-conversion-gate01/85/Database-Modeling-Using-Entity-Weak-And-Strong-Entity-Types-10-320.jpg)
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Database Modeling Using Entity.. Weak And Strong Entity Types
- 1. Database Modeling Using Entity Weak And Strong Entity Types
- 2. Data Modeling Data modeling : A technique for organizing and documenting a system’s DATA. Data modeling is sometimes called database modeling because a data model is usually implemented as a database. It is sometimes called information modeling. Entity relationship diagram (ERD) : A data model utilizing several notations to depict data in terms of the entities and relationships described by that 2
- 3. Process of creating a data model for an information system by applying formal data modeling techniques. Process used to define and analyze data requirements needed to support the business processes. 3 Data Modeling
- 4. “ One way to structure unstructured problems is to Draw Models ” 4
- 5. Why is data modeling considered crucial? Data is viewed as a resource to be shared by as many processes as possible. As a result, data must be organized in a way that is flexible and adaptable to unanticipated business requirements – and that is the purpose of data modeling. 5
- 6. What is Data Model Data Model is a collection of conceptual tools for describing data, data relationships, data semantics and consistency constraint. It provides a way to describe the design of a database at the physical, logical and view levels. 6
- 7. Conceptual : describes WHAT the system contains Logical : describes HOW the system will be implemented, regardless of the DBMS Physical : describes HOW the system will be implemented using a specific DBMS 7 Different Data Models
- 8. There are several notations for data modeling, but the actual model is frequently called an entity relationship diagram (ERD). An ERD depicts data in terms of the entities and relationships described by the data 8 Data Modeling
- 10. Data Model Elements 10 ER models have the following core concepts Entity – A concept to abstractly represent all instances of a group of similar ‘things. An entity is a class of persons, places, objects, events, or concepts about which we need to capture and store data. An entity instance is a single occurrence of an entity. Attribute – a descriptive property or characteristic of an entity. It is a simple, atomic data item like a date, a name, a number [also called Property or Field ]
- 11. Data Model Elements 11 A compound attribute is one that actually consists of more primitive attributes. Synonyms in different data modeling languages are numerous: concatenated attribute, composite attribute, and data structure. Relationship – an association that exists between one or more entities. The relationship may represent an event that links the entities or merely a logical affinity that exists between the entities.
- 12. Data Model Elements 12 Attributes Domains: The values for each attribute are defined in terms of three properties: data type, domain, and default. The data type for an attribute defines what class of data can be stored in that attribute. An attribute’s data type determines its domain. The domain of an attribute defines what values an attribute can legitimately take on. Every attribute should have a logical default value. The default value for an attribute is that value which will be recorded if not specified by the user.
- 13. Data Model Elements 13 Attributes identification: Every entity must have an identifier or key. An key is an attribute, or a group of attributes, which assumes a unique value for each entity instance. It is sometimes called an identifier. A group of attributes that uniquely identifies an instance of an entity is called a concatenated key. Synonyms include composite key and compound key A primary key is that candidate key which will most commonly be used to uniquely identify a single entity instance. Any candidate key that is not selected to become the primary key is called an alternate key.
- 14. Data Model Elements 14 Cardinality: Each relationship on an ERD also depicts the complexity or degree of each relationship and this is called cardinality. Cardinality defines the minimum and maximum number of occurrences of one entity for a single occurrence of the related entity. Because all relationships are bi-directional, cardinality must be defined in both directions for every relationship.
- 15. Given that … “Customer” is an entity. “Product” is an entity. For a “Customer” we need to know their “customer number” attribute and “name” attribute. For a “Product” we need to know the “product name” attribute and “price” attribute. “Sale” is an entity that is used to record the interaction of “Customer” and “Product”. 15 Example
- 16. Why and When The purpose of a data model is to describe the concepts relevant to a domain, the relationships between those concepts, and information associated with them 16
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- 19. Definition The entity set which does not have sufficient attributes to form a primary key is called as Weak entity set. An entity set that has a primary key is called as Strong entity set 19
- 20. “ ” The relationship between weak entity and strong entity set is called as Identifying Relationship. 20
- 21. A weak entity set is represented by doubly outlined box and corresponding identifying relation by a doubly outlined diamond Here double lines indicate total participation of weak entity in strong entity set it means that every payment must be related via loan-payment to some account. The arrow from loan-payment to loan indicates that each payment is for a single loan. The discriminator of a weak entity set is underlined with dashed lines rather than solid line. 21 Concepts
- 22. Concepts The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent plus the weak entity sets discriminator. In the above example {loan_number, payment_number} acts as primary key for payment entity set. A member of a strong entity set is called dominant entity and member of weak entity set is called as subordinate entity 22
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