Relational Database
Data organized as tables with declared relationships, queried declaratively and guarded by constraints.
A relational database stores data as tables of rows and columns, with relationships expressed by keys and integrity enforced by declared constraints. It is queried declaratively: you describe the result you want and the engine chooses how to obtain it.
Its enduring advantage is that correctness can be delegated to the schema. A foreign key, a uniqueness constraint, or a not-null declaration is enforced for every writer, including the ones written years later by people who never read the original code. Application-level validation protects only the paths that go through it.
Transactions are the second pillar: a set of changes either all happen or none do, which is what makes multi-step operations safe under concurrency and failure.
Two things worth holding onto when working through an abstraction layer. The layer's update semantics are usually partial — an absent key means "leave this column alone", not "clear it" — so clearing a field means writing an explicit null, and deleting a key from an object before saving is a no-op that in-memory tests happily pass. And a mirrored copy of a database in an analytics warehouse can carry duplicate rows from the synchronization process, so any count taken there should be de-duplicated before it is trusted.
See also11
Multi-Tenancy
One deployment serving many isolated customers, with tenancy threaded through data, routing, and access.
Data & Content12 connections
Seed Data
Initial content created programmatically to make an empty system usable or demonstrable.
Data & Content14 connections
Database Migration
A versioned, ordered change to a database schema, applied once and recorded.
Data & Content20 connections
Schema Drift
Divergence between a schema and the code, types, or documentation that describe it.
Data & Content16 connections
Draft and Published
Keeping an in-progress version of content separate from the live one, with all the state that implies.
Data & Content6 connections
Idempotence
The property that performing an operation twice has the same effect as performing it once.
Systems & Tooling34 connections
Headless CMS
A content system exposing structured data through an API, with presentation left entirely to consumers.
Data & Content12 connections
Feature Flag
A runtime switch that decouples shipping code from enabling behavior.
Data & Content19 connections
SQLite
A complete SQL database packaged as a small library that stores everything in one file, public domain since 2000, tested to an extreme standard, and probably the most widely deployed database in the world.
Data & Content9 connections
WordPress
The open-source PHP publishing system forked from b2 in 2003 that grew from a blogging tool into the software behind a large share of all websites, held together by themes, plugins, and a strict commitment to backward compatibility.
Web Platform12 connections
Object-Relational Mapping
A library that lets code treat database rows as ordinary objects, saving a great deal of boilerplate at the cost of hiding the queries that actually run.
Data & Content9 connections
Linked from21
- ACIDData & Content
The four guarantees a transactional database makes so concurrent, interrupted work never leaves data half-done.
- B-TreeComputation & Algorithms
A self-balancing tree with many children per node, designed to minimize the number of disk reads a lookup costs.
- Database ConstraintData & Content
Rules declared in the schema that the database itself enforces on every write, such as uniqueness, required values, and allowed ranges, so bad data is refused at the door rather than cleaned up later.
- Database MigrationData & Content
A versioned, ordered change to a database schema, applied once and recorded.
- DenormalizationData & Content
Deliberately duplicating data to make reads faster, trading update complexity for query simplicity.
- Draft and PublishedData & Content
Keeping an in-progress version of content separate from the live one, with all the state that implies.
- Feature FlagData & Content
A runtime switch that decouples shipping code from enabling behavior.
- Foreign KeyData & Content
A column that points at a row in another table, with the database refusing any change that would leave the pointer dangling.
- Hash TableComputation & Algorithms
A key-value structure that uses a digest of the key to index an array of buckets.
- Headless CMSData & Content
A content system exposing structured data through an API, with presentation left entirely to consumers.
- IdempotenceSystems & Tooling
The property that performing an operation twice has the same effect as performing it once.
- Key-Value StoreData & Content
The simplest kind of database, which stores opaque values under unique keys and supports little more than get, put and delete, trading query power for speed and easy scaling.
- Multi-TenancyData & Content
One deployment serving many isolated customers, with tenancy threaded through data, routing, and access.
- Object-Relational MappingData & Content
A library that lets code treat database rows as ordinary objects, saving a great deal of boilerplate at the cost of hiding the queries that actually run.
- PHPWeb Platform
The server-side language that began in 1994 as a personal set of homepage tools, spread on cheap shared hosting to run much of the web including WordPress and early Facebook, and survived years of ridicule by getting much faster and stricter.
- Schema DriftData & Content
Divergence between a schema and the code, types, or documentation that describe it.
- Seed DataData & Content
Initial content created programmatically to make an empty system usable or demonstrable.
- SQLData & Content
The declarative language for asking questions of relational databases, designed at IBM in the 1970s, standardized in 1986, repeatedly declared obsolete and still the most widely used way to read and write structured data.
- SQLiteData & Content
A complete SQL database packaged as a small library that stores everything in one file, public domain since 2000, tested to an extreme standard, and probably the most widely deployed database in the world.
- WordPressWeb Platform
The open-source PHP publishing system forked from b2 in 2003 that grew from a blogging tool into the software behind a large share of all websites, held together by themes, plugins, and a strict commitment to backward compatibility.
- Write-Ahead LoggingComputation & Algorithms
Recording the intent of a change durably before applying it, so a crash can be recovered.