# Architecture principles whose type is constraint

> 37 records

This index as JSON: https://banes-lab.com/json/api/facets/architecture/type/constraint

## Entries

- [Bounded Context](https://banes-lab.com/records/architecture/bounded-context.md): A rule or precondition that each domain model holds inside one explicit boundary, where its terms have one meaning.
- [Event Ordering](https://banes-lab.com/records/architecture/event-ordering.md): A rule or precondition that a stateful consumer processes the events of one key in their sequence order.
- [Directed Acyclic Graph (DAG)](https://banes-lab.com/records/architecture/directed-acyclic-graph.md): A rule or precondition that every dependency points one way and the graph they form has no cycle, so its nodes can be put in topological order.
- [API Contract](https://banes-lab.com/records/architecture/api-contract.md): A rule or precondition that each endpoint declares its request, response and error shapes in a versioned schema.
- [Service Contract](https://banes-lab.com/records/architecture/service-contract.md): A rule or precondition that a service declares its operations, their results and their side effects to every consumer.
- [Data Contract](https://banes-lab.com/records/architecture/data-contract.md): A rule or precondition that data exchanged between parties has declared fields, types, nullability and meaning.
- [Schema Contract](https://banes-lab.com/records/architecture/schema-contract.md): A rule or precondition that every payload is validated against a machine-readable schema at the boundary it crosses.
- [Semantic Contracts](https://banes-lab.com/records/architecture/semantic-contracts.md): A rule or precondition that each term and value at a boundary has one agreed meaning, beyond its type.
- [Preconditions](https://banes-lab.com/records/architecture/preconditions.md): A rule or precondition that must hold on an operation's input and state before the operation runs.
- [Postconditions](https://banes-lab.com/records/architecture/postconditions.md): A rule or precondition that an operation's result and resulting state must satisfy when it returns.
- [Invariant](https://banes-lab.com/records/architecture/invariant.md): A rule or precondition that holds for an entity or aggregate in every state it can reach.
- [Backward Compatibility](https://banes-lab.com/records/architecture/backward-compatibility.md): A rule or precondition that a new version keeps working for consumers written against an older one.
- [Forward Compatibility](https://banes-lab.com/records/architecture/forward-compatibility.md): A rule or precondition that an older reader accepts data from a newer writer by ignoring the fields it does not know rather than failing on them.
- [Protocol Compatibility](https://banes-lab.com/records/architecture/protocol-compatibility.md): A rule or precondition that both ends of a connection speak a declared protocol version they both support.
- [Uniform Interface](https://banes-lab.com/records/architecture/uniform-interface.md): A rule or precondition that every resource in an API uses the same verbs, response shapes and error format.
- [Consumer-Driven Contracts](https://banes-lab.com/records/architecture/consumer-driven-contracts.md): A rule or precondition that a provider verifies each change against the expectations its consumers have recorded.
- [Standards Compliance](https://banes-lab.com/records/architecture/standards-compliance.md): A rule or precondition that an implementation conforms to the published standard for its protocol, format or domain.
- [SLO/SLI](https://banes-lab.com/records/architecture/slo-sli.md): A rule or precondition that a service's reliability is stated as a measured indicator with an objective and an error budget over a window.
- [Forward-Only Processing](https://banes-lab.com/records/architecture/forward-only-processing.md): A rule or precondition that a stream is read once in order, keeping only rolling state, so no decision ever needs to revisit earlier input.
- [Compliance](https://banes-lab.com/records/architecture/compliance.md): A rule or precondition that a system implements the controls a regulation or standard requires, and keeps evidence of each one.
- [Declared Subject](https://banes-lab.com/records/architecture/declared-subject.md): A rule or precondition that a record carries an allocated id and a declared subject key as two fields, so a moved surface keeps the id, a renamed subject keeps the key, and two records sharing a key are a finding.
- [Operand-Free Outcome Surface](https://banes-lab.com/records/architecture/operand-free-outcome-surface.md): A rule or precondition that a surface carrying one jointly authored product declares that one writer per record has no operand there, and settles a collision by announcement and by each author cutting its own duplicate.
- [Projection Channel](https://banes-lab.com/records/architecture/projection-channel.md): A rule or precondition that the projection a host injects into every bounded reader is refreshed in the same change as the fact it carries, in a shape a check reads.
- [Section Lifetime Divergence](https://banes-lab.com/records/architecture/section-lifetime-divergence.md): A rule or precondition that a file states a default lifetime and each section declares only the axes on which it differs, since the narrower unit is the more constrained one.
- [Reversible Channel Encoding](https://banes-lab.com/records/architecture/reversible-channel-encoding.md): A rule or precondition that a channel name is a total and invertible encoding of the scope it belongs to, with an alphabet that excludes the separator, so a retention check can read the scope back out of the name.
- [Fan-In Ceiling](https://banes-lab.com/records/architecture/fan-in-ceiling.md): A rule or precondition that the useful number of parties is bounded by the fan-in of the most contended surface, where claims resting on it go stale faster than they help.
- [State-Arity Limit](https://banes-lab.com/records/architecture/state-arity-limit.md): A rule or precondition that a property relating two states of content, such as growing but never shrinking, is enforced only by a mechanism holding both readings, in the layer that already spans runs.
- [Joinable Mandated Field](https://banes-lab.com/records/architecture/joinable-mandated-field.md): A rule or precondition that a mandated field takes a value from a closed set or an identifier, or declares that it is written for readers, so a governed surface never looks measured on a property nothing can read.
- [Single Aggregate](https://banes-lab.com/records/architecture/single-aggregate.md): A rule or precondition that a shared measurement keeps one aggregate, overwritten by each run that can honestly replace it, while a run that cannot streams its verdict instead of writing a second report.
- [Concern-Folder Correspondence](https://banes-lab.com/records/architecture/concern-folder-correspondence.md): A rule or precondition that a file's concern tag matches the label of the folder that holds it.
- [Bounded Nesting Depth](https://banes-lab.com/records/architecture/bounded-nesting-depth.md): A rule or precondition that a file sits within a fixed number of folders below its governed root, with each folder taking a later role than the one above it.
- [Set-Relative Member Name](https://banes-lab.com/records/architecture/set-relative-member-name.md): A rule or precondition that a file inside a subject folder names only its own subject, because the folder already names the set.
- [Mirrored Test Placement](https://banes-lab.com/records/architecture/mirrored-test-placement.md): A rule or precondition that a test sits in the concern folder of the file it tests, under a test root mirroring that file's governed root, and moves whenever that file moves.
- [Sanctioned Generic Subject](https://banes-lab.com/records/architecture/sanctioned-generic-subject.md): A rule or precondition that a file takes the one generic subject only when it is generic over its type parameters and names no domain noun anywhere in its source.
- [Root Spine Files](https://banes-lab.com/records/architecture/root-spine-files.md): A rule or precondition that a governed root carries only its entry document and its accumulators at the root, and every other file sits in a concern folder.
- [Transaction Boundary](https://banes-lab.com/records/architecture/transaction-boundary.md): A rule or precondition that a transaction covers exactly the writes of one unit of work inside one service.
- [Isolation](https://banes-lab.com/records/architecture/isolation.md): A rule or precondition that concurrent transactions do not see each other's uncommitted changes, to the degree the isolation level declares.