ER diagrmas introduction
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| Entity | Represents a place, a thing, a person you want to track in a database. This will become a table in a database
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| entity instance | Each occurrence of the entity
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| attribute | Describes various characteristics about an individual entity
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| primary key | A special attribute that make it so that no two rows will have the same value for that attribute
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| relationship | Describes how one or more entities interact with each other
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| cardinality | The count of instances that are allowed or are necessary between entity relationships
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| ERD Entity Relationship diagram | Graphical representation of the data requirements for a data base
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| composite key | When you need more than one attribute to make each instance unique
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| mandatory | means that you must have at least one instance in the relationship
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| mandatory |
means that you must have at least one instance in the relationship
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| Entity | basically is a container: all the elements that are like it are grouped together under it
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| Generalization |
in a “bottom up” design, is an entity that represents a superset of other entities
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| Specialization | in a “top down” design, is an entity that represents a subset of another entity
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| incomplete | Specialization where only some individuals of the parent entity are specialized
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| complete | Specialization where all individuals of the parent entity are specialized (have one or more unique attributes that are not common to the parent).
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| overlapping | Specialization where an individual of the parent entity may be a member of more than one of the specialized entities.
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| disjoint | (also called an exclusive specialization). When an individual of the parent entity may be a member of only one specialized entities.
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| one to many relationship | In a one-to-many relationship between Table A and Table B, each row in Table A is linked to 0, 1 or many rows in Table B
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| many to many relationship | Refers to the relationship between two entities A and B in which A may contain a record for which there are many records B and vice versa
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| one to one relationship | relationship between two entities A and B in which one element of A may only be linked to one element of B, and vice versa
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Review the information in the table. When you are ready to quiz yourself you can hide individual columns or the entire table. Then you can click on the empty cells to reveal the answer. Try to recall what will be displayed before clicking the empty cell.
To hide a column, click on the column name.
To hide the entire table, click on the "Hide All" button.
You may also shuffle the rows of the table by clicking on the "Shuffle" button.
Or sort by any of the columns using the down arrow next to any column heading.
If you know all the data on any row, you can temporarily remove it by tapping the trash can to the right of the row.
To hide a column, click on the column name.
To hide the entire table, click on the "Hide All" button.
You may also shuffle the rows of the table by clicking on the "Shuffle" button.
Or sort by any of the columns using the down arrow next to any column heading.
If you know all the data on any row, you can temporarily remove it by tapping the trash can to the right of the row.
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Created by:
annap
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