An ERD displays tables and relationships between those (Cool web site)
An ERD displays tables and relationships between those tables. Figure 3-10 shows an example ERD for tables in a schema containing published books. Figure 3-10 shows what an ERD is and what it looks like. ERDs are simple. There is nothing complicated or inscrutable about ERDs. A table is often referred to as an entity in an ERD. Figure 3-10: An Entity Relationship Diagram (ERD). At this point, you don t need to understand how relationships are created between the tables shown in Figure 3-10. Creating the relations is a little too advanced for this chapter and will be covered in later chapters, mostly in Chapter 4. Crows Foot A crow s foot is used to describe the many side of a one-to-many or many-to-many relationship, as highlighted in Figure 3-11. A crow s foot looks quite literally like the imprint of a crow s foot in some mud, with three splayed toes. (How many toes a crow has exactly I am not sure.) By now, you should get the idea that many toes implies more than one and thus many, regardless of how many toes a crow actually has. Figure 3-11 shows a crow s foot between the AUTHOR and PUBLICATION tables, indicating a one-to-many relationship between AUTHOR and PUBLICATION tables. Publisher publisher_id name Author author_id name Subject subject_id parent_id title Publication publication_id subject_id (FK) author_id (FK) title Review review_id publication_id (FK) review_id (FK) text CoAuthor coauthor_id (FK) publication_id (FK) Edition ISBN publisher_id (FK) publication_id (FK) print_date pages list_price format rank ingram_units 50 Chapter 3
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