When creating a new database, schemas will commonly be used to try to simplify the layout of the database to an easy-to-read manner. There are multiple different kinds of schemas, including Entity-Relationship Diagrams. This type of schema is a higher-level schema type that adds more detail to the schema for later use and better understanding.
When working with an Entity Relationship Diagram, squares will commonly be found within the diagram and are used to represent Entities within the database. The term entities is another name for tables within the database.
When working with an ERD, ovals will commonly be seen throughout the diagram to represent attributes. Attributes are the columns that are inside of a table, meaning that attributes will commonly be connected to entities.
When working with an Entity Relationship Diagram, diamonds will typically be seen throughout the diagram and are used to represent actions. Actions are used to help give more detail regarding the relationship between entities within the diagram.
When working with an Entity Relationship Diagram, connecting lines will be seen consistently within the diagram, and is used to show the relationships between items within the Entity Relationship Diagram.
When working with an Entity Relationship Diagram, connecting lines will sometimes have symbols on the ends next to entities. These symbols are called cardinality and are used to add even more detail to the diagram regarding the kind of relationship that exists between entities in the database.
Three-tier architecture is a design philosophy that splits an application into three parts. This is done to assist with the development and helps with the scalability of an application. The three tiers are the presentation, application, and data tiers.
In an application that uses a three-tier architecture, the presentation tier is used to represent the user interface of the application. This includes all data gathering and anything else that the user might see or interact with within the application.
When working on an application that uses a three-tier architecture, the application tier is the tier that does all of the data processing and connects the presentation tier to the data tier. This is typically where the bulk of the application will go.
In an application that uses a three-tier architecture, the data tier is the layer responsible for storing all of the data for the application. No data manipulation occurs at this tier as it is strictly for storing data.
When creating an application with the idea of using tiers, not every project needs to use three tiers. Two-tier applications exist and can be created, and there can easily be more than three tiers if needed. This means there is no wrong or right answer to the number of tiers an application can have as it’s dependent on the application itself.