Know How to Read an ER Model

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Software applications store data in databases. Database administrators, system architects and developers design the layout. The ER model is the visual of how the data is stored. An ER model is an entity relationship model.
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Reading a data model is like reading a map; most elements of a map are instantly recognizable and give the viewer a visual sense of where they are. In databases, the Entity-Relationship (ER) model gives the viewer a visual sense of the data model. Reading an ER model, like reading a map, can be done just for basic information and then, as you become accustomed to reading, you can look deeper for the finer intricacies of the model.
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Being able to read and ER model is like reading a map; some elements of a map are more readily understandable. Learning to read an ER model is like other information we learn, it helps to start with a over view and continue learning with understanding the finer points and intricacies.
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The "E" of the ER model refers to ''entity''; an entity is also referred to as a table. The tables in a database store the data. For example, imagine a database that stores customer information. The tables in a customer database might consist of a customer table, an address table and a phone number table. Each table contains one or more columns.
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An entity is also referred to as a table, tables store data. For example, imagine a database that stores customer information. The tables in a customer database might consist of a customer table, an address table and a phone number table.
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The "R" of the ER model refers to the ''relationships'' the tables have to each other. Imagine a database that stores customer and sales information. The customer table would have a relationship to the sales tale. In order to tie the two tables together and join the information, a column in the sales table must contain a reference to the associated customer. These table relationships are shown on an ER model, which in this case would be a line between the customer and sales tables.
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The R of the ER model refers to the relationships, the relationships the tables and data have to each other. Each table has columns. Each column represents a data field, from the application, the same data entry fields we see in an application are the fields we’ll find on the ER model.
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As a map shows places, an ER model shows tables. Once you become comfortable reading the tables on an ER model, a next level of understanding is reading the relationships. As a map shows us how to navigate from one place to another, an ER model shows how the tables relate to one another. Primary keys and foreign keys are two types of relationships usually shown on an ER model.
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Using our customer database example, the columns on a customer table might include: company name, company website and company president. The address table might include these columns of data: street name, suite number, city, state and zip code.
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A primary key is used to uniquely identify each row in each table. The primary key is comprised of a single column or, less frequently, a set of columns. No two rows can have the same value for the primary key. An example would be using the customer name field as the primary key on the customer table.
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As each company gets added or created through the application, a row of information for that company gets added to the tables. Columns and rows in a database can be compared to an Excel file where the column headers represent what data is stored and each row of the spreadsheet represents the data itself. Tables in a database are made up of columns and rows.
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A foreign key is a referential constraint between two tables. The foreign key identifies a column or a set of columns as a reference to another table. Using the customer database example, a column on the address table is needed to refer back to the customer table. Foreign keys link data and tables together.
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A primary key is used to uniquely identify each row in each table. The primary key is comprised of a single column or set of columns. No two rows can have the same value for the primary key. An example would be using the customer name field as the primary key on the customer table.
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A foreign key is a referential constraint between two tables. The foreign key identifies a column or a set of columns as a reference to another table. Using the customer database example, a column on the address table is needed to refer back to the customer table. This relationship links the data and the tables together.
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Having a sense of the data model is like knowing the primary highways through a state or province. Once you get familiar with reading a data model, you’ll find you won’t want to work with an application without seeing the ER model. It would be like leaving your house without at GPS or road atlas – the data model is the navigation tool into the inner working of an application and its data.
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Having a sense of the data model is like knowing the primary highways through a state or province. Once you get familiar with reading a data model, you’ll find you won’t want to work on an application without seeing the model. It would be like leaving your house without at GPS or road atlas – the data model is navigation tool into the inner working of an application.
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Current revision

Reading a data model is like reading a map; most elements of a map are instantly recognizable and give the viewer a visual sense of where they are. In databases, the Entity-Relationship (ER) model gives the viewer a visual sense of the data model. Reading an ER model, like reading a map, can be done just for basic information and then, as you become accustomed to reading, you can look deeper for the finer intricacies of the model.

The "E" of the ER model refers to entity; an entity is also referred to as a table. The tables in a database store the data. For example, imagine a database that stores customer information. The tables in a customer database might consist of a customer table, an address table and a phone number table. Each table contains one or more columns.

The "R" of the ER model refers to the relationships the tables have to each other. Imagine a database that stores customer and sales information. The customer table would have a relationship to the sales tale. In order to tie the two tables together and join the information, a column in the sales table must contain a reference to the associated customer. These table relationships are shown on an ER model, which in this case would be a line between the customer and sales tables.

As a map shows places, an ER model shows tables. Once you become comfortable reading the tables on an ER model, a next level of understanding is reading the relationships. As a map shows us how to navigate from one place to another, an ER model shows how the tables relate to one another. Primary keys and foreign keys are two types of relationships usually shown on an ER model.

A primary key is used to uniquely identify each row in each table. The primary key is comprised of a single column or, less frequently, a set of columns. No two rows can have the same value for the primary key. An example would be using the customer name field as the primary key on the customer table.

A foreign key is a referential constraint between two tables. The foreign key identifies a column or a set of columns as a reference to another table. Using the customer database example, a column on the address table is needed to refer back to the customer table. Foreign keys link data and tables together.

Having a sense of the data model is like knowing the primary highways through a state or province. Once you get familiar with reading a data model, you’ll find you won’t want to work with an application without seeing the ER model. It would be like leaving your house without at GPS or road atlas – the data model is the navigation tool into the inner working of an application and its data.

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