              
Qt Contacts SchemaIntroductionThe Qt Contacts API makes use of detail leaf classes which provide certain well-known functionality. In order to develop a backend engine which can service clients or provide synchronization to other backends, the schema must be known. The schema provided by the Qt Contacts API is updated with every release of Qt Mobility, so the function which returns the default schema definitions can take an integer which identifies the schema version which the engine writer developed against. Engine writers should call schemaDefinitions() in their code which generates the manager-specific schema (which is returned to clients when they call QContactManager::detailDefinitions()). The schemaDefinitions() function should NOT be called by clients; rather, clients should call QContactManager::detailDefinitions() instead. Schema DefinitionDifferent backends have different capabilities. Some backends may not be able to implement certain definitions in the default schema (for example, some backends might not have support for storing location information), while other backends may not be able to implement some aspects of a particular definition in the default schema (for example, a logo field for organization details). In order to be useful for clients, however, all backends should attempt to support the default schema. Furthermore, no backend should support a schema definition of a modified form where those modifications change the semantics of the data. A client should be able to request details of the QContactPhoneNumber type (that is, details whose definition name is "PhoneNumber") with reasonable certainty that the data returned is a phone number. By implementing the default schema, the backend developer ensures that client code written against the default schema will work without source modification against their backend. Default SchemaThe leaf details that form the current version of the default schema are as follows:
Note that the following leaf details were added to the default schema in version 1.1 of the Qt Mobility project: Detail Definition UniquenessA uniqueness constraint on a detail definition means that for any QContact, only one detail of that definition may be saved. The leaf classes which have a uniqueness constraint in the default schema are as follows: Detail Access ConstraintsSome details in a contact retrieved from a manager may have access constraints set. An access constraint on a detail means that the detail may not be removed (if the access constraint is QContactDetail::Irremovable) or updated (if the access constraint is QContactDetail::ReadOnly) by the client. If the client attempts to save an updated version of a read-only detail in a contact, or remove a detail which is irremovable from a contact, the operation will succeed; however those updates to the contact will be ignored by the manager when the contact is saved there. For example, the QContactDisplayLabel is defined in the default schema as a read-only, irremovable detail, meaning that it may not be modified or deleted by the client, but are provided by the backend (in the case of QContactDisplayLabel, automatically synthesized by the backend from various details of the contact, like the QContactName, QContactNickname, etc). There are three possible detail access constraints: read-only, irremovable and no constraint. A read-only constraint ensures that clients cannot modify the values stored in such details in the persistent copy of the contact (that is, the contact as it is stored in the manager); the irremovable constaint ensures that a particular detail may not be removed by clients. In general, most details which are read only will also be irremovable, and vice versa. One exception to this is the QContactType detail, which is irremovable but may be updated by clients as desired. Details with no constraint may be added, updated and removed as desired by the client. Changes to such details in a contact will be persisted in the manager when the client calls QContactManager::saveContact(). Please see the documentation of QContactDetail for more information on access constraints. The leaf classes which have access constraints in the default schema are as follows:
Furthermore, in the default schema, every contact is required to have at least two details by default: a QContactType which describes the type of entity that the contact represents (for example, a person or a group), and a QContactDisplayLabel which holds the default display label for the contact. Backend-provided DetailsAs described in the section on detail access constraints, some details are provided by the backend, such as QContactDisplayLabel and QContactPresence. When the client attempts to save a QContact that contains these details, these details will be ignored by the backend (since any values in this field are synthesized by the backend). This means that while clients may (for example) add a QContactPresence detail to a QContact, it will not be persisted in the manager when the client attempts to save that contact. Precisely which details are backend-provided is backend specific; some backends provide more details than others. X
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