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Glossary
Look up any term from the course. Each entry links back to the lesson that taught it.
| Term | Definition | Lesson |
|---|---|---|
| Alternate key | An alternate key is a candidate key that was not chosen as the primary key. | Choosing Good Primary Keys |
| Attribute | An attribute is a fact stored about an entity; in a finished table it appears as a field (a column). | Fields and Records |
| Candidate key | A candidate key is a column, or combination of columns, that could uniquely identify each row in a table. | Choosing Good Primary Keys |
| CardinalityAlso ONE and MANY | Cardinality is the count of related records on each side of a relationship: one-to-one, one-to-many, or many-to-many. | One-to-Many |
| Composite key | A composite key is a primary key that uses more than one column together to uniquely identify a row. | Choosing Good Primary Keys |
| Data | Data is a collection of raw, unprocessed facts, numbers, words, or observations. | What Is Data? |
| Data integrity | Data integrity is the accuracy, completeness, and consistency of stored data, enforced by rules that must always be true. | Data Integrity and Invalid Data |
| Data type | A data type is the kind of data a field may hold — such as text, number, or date/time — and it determines what operations can be performed on that field. | Data Types |
| Database | A database is an organised collection of related data, stored electronically so it can be accessed, managed, and kept secure. | What is a Database? |
| Database design | Database design is the process of dividing information into subject-based tables, providing the means to join those tables, and setting rules that protect the accuracy and integrity of the data. | Designing a Database |
| Database management system (DBMS)Also DBMS | A database management system (DBMS) is the software that organises a database and controls access to the data stored in it. | Database Management System |
| Delete anomaly | A delete anomaly is when deleting a row you no longer need also destroys information you still required. | Redundant Data and Anomalies |
| Domain integrity | Domain integrity is the rule that every value in a column must belong to the allowed set for that field — the correct type, format, range, or list. | Data Integrity and Invalid Data |
| Duplicated data | Duplicated data is the same fact stored in more than one place, which wastes space and increases errors and inconsistencies. | Duplicated Data |
| Entity | An entity is a major subject about which data is stored, such as members or books; each entity becomes a table. | Entities |
| Entity integrity | Entity integrity is the rule that every row can be uniquely identified: the primary key is unique and is never empty. | Data Integrity and Invalid Data |
| Entity-relationship diagramAlso ER diagram | An entity-relationship (ER) diagram is a picture of the entities in a database and the relationships among them. | ER Diagrams |
| FieldAlso Column | A field is one column in a table: a single item of information that appears in every record. | Fields and Records |
| Filter | A filter is a condition that returns only the rows that match it; unmatched rows remain stored in the table. | Asking Questions of Data |
| First normal form (1NF)Also 1NF | A table is in first normal form (1NF) when each field holds a single value and there are no repeating groups of columns. | Normalisation |
| Foreign keyAlso FK | A foreign key is another table’s primary key, stored in this table so that the two tables can be related. | Foreign Keys |
| Functional dependency | A functional dependency exists when the value of one field (or set of fields) determines the value of another field. | Normalisation |
| Index | An index is a lookup structure the database keeps for a field so it can find matching rows without reading every record in the table. | Indexing |
| Information | Information is data that has been processed and given context so that it has meaning. | Data vs Information |
| Insert anomaly | An insert anomaly is when you cannot record a needed fact until some other, unrelated fact exists. | Redundant Data and Anomalies |
| Junction tableAlso Link table, Intermediate table | A junction table is a third table that represents a many-to-many relationship by storing the primary keys of both related tables, splitting it into two one-to-many relationships. | Many-to-Many and Junction Tables |
| Many-to-many | In a many-to-many relationship, each record in either table can match many records in the other table. | Many-to-Many and Junction Tables |
| Normalisation | Normalisation is the process of organising data into tables and relationships according to rules designed to eliminate redundancy and inconsistent dependency. | Normalisation |
| One-to-many | In a one-to-many relationship, one record in one table can match many records in another table, while each of those records matches only one record on the first side. | One-to-Many |
| One-to-one | In a one-to-one relationship, each record in one table matches at most one record in the other table. | One-to-One |
| Orphan record | An orphan record is a row whose foreign key does not match any primary key in the related table. | Orphan Records and Referential Integrity |
| Primary keyAlso PK | A primary key is a column, or set of columns, that uniquely identifies each row stored in a table. | Primary Keys |
| Query | A query is a request for data results from a database, or for an action on the data, or for both. | Asking Questions of Data |
| RecordAlso Row | A record is one row in a table: a complete, consistent set of facts about one instance of the table’s subject. | Fields and Records |
| Redundant data | Redundant data is the same fact stored more than once, which wastes space and increases the likelihood of errors and inconsistencies. | Redundant Data and Anomalies |
| Referential integrity | Referential integrity is the rule that every foreign-key value must match a primary-key value in the related table. | Orphan Records and Referential Integrity |
| Relational database | A relational database is a database that organises data into tables of rows and columns, where related facts in different tables are connected by matching values. | Relational Database |
| Relationship | A relationship is how data in one table is related to data in another, created by pairing a primary key with a foreign key. | How Keys Connect Tables |
| Second normal form (2NF)Also 2NF | A table is in second normal form (2NF) when it is in 1NF and every non-key field depends on the whole primary key, not on only part of it. | Normalisation |
| Sort | A sort is an order applied to records for display; it changes the order you see, not how the rows are stored. | Asking Questions of Data |
| Storing data | Storing data means keeping collected data organised and accessible so it can be found again and used later. | Why We Store Data |
| Table | A table is a subject-based list of data arranged in rows and columns. | What is a Table? |
| Third normal form (3NF)Also 3NF | A table is in third normal form (3NF) when it is in 2NF and no non-key field depends on another non-key field — each depends on the primary key and nothing else. | Normalisation |
| Update anomaly | An update anomaly is an inconsistency that occurs when the same fact is stored in several places and changing it does not update every copy. | Redundant Data and Anomalies |
| Validation | Validation is checking data against rules as it is entered, so that only values that meet those rules can be saved. | Validation |
| Value | A value is the actual data stored at the intersection of one record and one field. | Fields and Records |
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