Tuesday, May 30, 2017

Physical ERD Diagrams

Physical ERDs are a bit more intuitive than logical diagrams. They account for the attribute type for each attribute within an entity. For this reason, they are often more complete and complex than a logical diagram but offer more information at the same time and can offer better insight about how a database is meant to be used and how it will store data.

In this hypothetical database which is meant to support analyzing historical home sales and proximity to parks. The parcel data and the sales data must be linked to one another to start the analysis and this has been shown in the physical ERD above. The various attributes have been distinguished by their data type so that the reader of this diagram can see how data will be represented within the database. Most attributes are based on a series of characters that are used to give each data item a unique identifier, such as the pin attribute on the parcels entity. For this reason, a VARCHAR data type is used since these attributes will neither be entirely numeric nor entirely text. The same idea is used to distinguish the other attributes based on how they need to be represented in accordance with their data characteristics.

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