versionhallintajärjestelmä

Versionhallinta, or version control, is a system that records changes to a set of files over time. It enables teams and individuals to track revisions, revert to previous states, and understand how a project evolves. A repository stores the project's files and the history of their modifications. Each change is captured in a commit, which includes metadata such as author, timestamp, and a message describing the modification. Branches allow parallel work streams, and merges integrate changes from different branches. Tags can mark important points such as releases. Integrity and reproducibility are supported by the system's data model, which often uses cryptographic checksums to detect accidental or malicious alterations.

Version control systems are broadly categorized as centralized or distributed. Centralized systems rely on a single central repository, while distributed systems copy the entire history to each client, facilitating offline work and robust collaboration. Examples include Subversion (centralized), Git and Mercurial (distributed), and Perforce (often used in large enterprises). Git has become the de facto standard in software development; hosting services such as GitHub, GitLab, and Bitbucket provide collaboration features, issue tracking, and continuous integration.

Typical workflows involve making changes in a working copy, committing them, and syncing with a remote repository. Branching supports feature work, experiments, and code reviews, with merges and conflict resolution when integrating changes. Version control is applicable beyond software—document management, data analysis, and digital media projects also benefit from its history tracking and collaboration features.