databasskjemaer

Databasskjemaer (database schemas) are the design blueprints that define the structure of a database. They specify how data is organized, including which tables exist, the columns within each table, the data types, and the relationships between tables. A databasskjema describes the metadata of the database, not the actual data stored in it.

Core elements include tables, columns, data types, and constraints. Keys are essential: primary keys uniquely identify each row; foreign keys enforce relationships to other tables. Additional constraints such as NOT NULL, UNIQUE, and CHECK ensure data integrity. Schemas may also define indexes, views, stored procedures, and triggers that influence data access and behavior.

Design process: A typical approach starts with a conceptual model (for example an entity–relationship diagram), moves to a logical schema that maps entities to tables and relationships, and ends with a physical schema tailored to a specific database system. Normalization aims to minimize redundancy by organizing data into related tables; common normal forms include 1NF, 2NF, and 3NF, while denormalization may be used for read performance.

Example: A simple relational schema might include a Customer table (CustomerID as primary key, Name, Email) and an Order table (OrderID as primary key, OrderDate, CustomerID as a foreign key). The foreign key links each order to a customer, enforcing referential integrity.

Evolution and scope: Schemas serve as a blueprint for a given database instance and guide data integrity, queries, and maintenance. They evolve through migrations or versioning as requirements change. In non-relational databases, schema definitions may be optional or enforced via validation rules rather than rigid tables.