## Introduction to ClubMS and Canonical APIs
**Club Management Software (ClubMS)** is a suite of software for managing fitness clubs: billing system, members management, group calendars, payments processing, personal trainers, etc. ClubMS is also know as Membership Management Software (MMS).
There are a lot of different ClubMS in the world, and they all have different domain models. Generally speaking, for a given fitness location, different services might be provided by different external ClubMS.
**Canonical API** hides this difference by mapping to EGYM Canonical Model. Implementation of Canonical API for a certain ClubMS service makes it compatible with EGYM Platform.
Some of the contracts in this Canonical API definition depend on multiple meta options. These meta options are not reflected by API parameters directly, but define conditional API contracts. Meta option values reflect ClubMS specifics and are provided by *Implementer of Canonical API*. EGYM Platform is then configured with these option values to enable integration with the given canonized service. **For example:** Different ClubMS use different types of credentials (security schemas) for their operations: client secret, chain secret, or location secret. Galaxy will expect corresponding configuration and pass appropriate parameters depending on corresponding meta option value.
The meta options are defined by a json schema that accompanies the yaml file (they should be sent together).
All conditional contracts that depend on specific meta option values are described in this Canonical API with references like `metaOption::someOptionName`. Implementer of Canonical API might want to remove all these conditional contracts and replace them by concrete contracts based on ClubMS specific meta option values (that should be known to the Implementer of Canonical API). String "metaOption::" can be used for quick finding of all such conditional contracts.