Relative Clauses in Technical Documentation

'That' is the standard relative pronoun for defining (restrictive) relative clauses referring to things. 'The service that handles authentication' identifies which specific service — it is a defining clause. 'Which' can also be used in defining clauses but 'that' is preferred in technical writing, especially in American English. 'Who' refers to people, not services or systems. 'Whose' expresses possession. Key rule: defining clauses (no commas) identify the noun and often use 'that' for things.

'Who' is the relative pronoun for people in both defining and non-defining clauses. 'The engineer who deployed the change' is a defining clause — it identifies which engineer. 'Which' and 'that' refer to things, not people. 'Whose' expresses possession ('the engineer whose PR was merged'). In technical incident reports and on-call escalations, 'the engineer who...' is the standard way to identify the person responsible for an action.

'Which' is the correct pronoun for non-defining (non-restrictive) relative clauses about things. The commas signal a non-defining clause — the information about 2022 is additional context, not identification. Non-defining clauses always use 'which' (not 'that') for things. 'That' cannot be used in non-defining clauses. 'Who' is for people. 'Whose' is for possession. In documentation, non-defining clauses add parenthetical information: 'The legacy module, which was written in 2018, will be deprecated next quarter.'

'That' is the preferred relative pronoun for defining clauses referring to things in technical writing. 'A load balancer that supports HTTP/2' defines the requirement — it specifies which type of load balancer is needed. This is the standard pattern in technical requirements documents: 'a system that handles X', 'a service that exposes Y', 'a library that supports Z'. 'For which' is grammatically correct in formal writing ('a load balancer for which HTTP/2 support is available') but is unnecessarily complex for this context.

'Whose' expresses possession — 'the team whose PR was approved' = 'the team, their PR was approved'. 'Whose' applies to both people and things in relative clauses. 'Who' would be used as a subject pronoun: 'the team who approved the PR' (different meaning). 'Which' and 'that' cannot express possession. 'Whose' is commonly used in code review comments, PR workflows, and access control documentation: 'the branch whose tests are passing', 'the service whose owner is listed in CODEOWNERS'.