Attributes are nouns that are listed with an entity

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Attributes are nouns that are listed with an entity. One or more attributes can serve as the entity identifier - the attribute(s) that can uniquely identify one instance of an entity. Concatenated identifier - several attributes are combined to uniquely identify an instance.
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39
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Relationships Relationships are associations between entities. Every relationship has a parent entity and a child entity. Relationships should be labeled with active verbs.
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Cardinality A relationship has cardinality which is the ratio of parent instances to child instances . The 1:1 relationship means that one instance of the parent entity is associated with one instance of the child entity. The 1:N relationship means that a single instance of a parent entity is associated with many instances of a child entity. The M:N relationship means that many instances of a parent entity can relate to many instances of a child entity.
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43 EMPLOYEE PARKING PLACE is assigned one-to-one is assigned to PRODUCT LINE PRODUCT includes one-to-many is included in STUDENT COURSE registers for many-to-many registers
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44 includes one-to-many one-to-one is included in Product ID - PK Prod Line ID - FK Prod Description Prod Line ID - PK Prod Line Descrip Emp ID - PK Emp Name Emp Address Parking ID - PK Emp ID - FK Location registers for many-to-many Student ID – PK Enrollment Student Name Student Address Course ID – PK Enrollment Code FK Course Name Course Descrip PRODUCT PRODUCT LINE EMPLOYEE PARKING PLACE is assigned to is assigned STUDENT COURSE registers
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Modality A relationship has modality of null or not null , which refers to whether or not an instance of a child entity can exist without a related instance in the parent entity Null means that an instance of a child entity can exist without a related instance in the parent entity Not Null means that an instance of a child entity can’t exist without a related instance in the parent entity
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Wednesday 10/18/17 Deliverable #1 (10/25), optional extension to 10/27 Exam #2 (10/23) Easier and (I)ndividual Harder and (G)roup Readings Now: CH 6 Next: none, exam & project work day
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Data Dictionary A data dictionary contains the information about the entities, attributes, and relationships on the ERD, or metadata . Metadata is data about data. Metadata is stored in the data dictionary so it can be shared by developers and users throughout the SDLC.
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Creating an ERD Drawing the ERD is an iterative process of trial and revision. 1. Identify the entities; 2. add the appropriate attributes to each entity; and 3. draw relationships among entities.
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Identifying Entities Entities represent the major categories of information that you need to store in your system.
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