By default, the database name is “Application_Registry_Service_DB_<GUID>”.  I’m not quite certain why, but I’m not so much a fan of the out of the box naming of databases with a GUID appended to the end – though I guess it does ensure that you’re never going to inadvertently create one on the fly that has the same name as others.

Similar to the BDC, the Application Registry Service database is read-heavy since there isn’t any writing done with the BDC . And though the services architecture is a bit more broken out, you can only have a single Application Registry Service per farm, which means that you can only have a single database associated with your farm, which in turn means get ready to watch it grow should you be migrating several BDCs into your farm while you prep them for conversion to Business Connectivity Services candidates.

Fortunately for scalability purposes, it is possible to mirror this database within a farm to ensure availability of data for the BDCs to operate, however it’s not possible to mirror the database or use log shipping to mirror the database onto another SQL instance. Perhaps keeping a backup handy would be helpful should the data become corrupted or your server’s SAN melt.

A visualization of the tables and associated columns is depicted here:

If you’re wondering what the tables and their associated columns look like for the Application Registry, then look no further as they are as follows:

Application_Registry_Service_DB_GUID
  AR_Action
    EntityId
    Icon
    Id
    IsDisplayed
    IsOpenedInNewWindow
    Position
    Url
  AR_ActionParameter
    ActionId
    Id
    Index
  AR_AdminLocks
    Id
    LockId
  AR_ApplicationRegistry
    Id
  AR_Association
    Id
  AR_AssociationMember
    AssociationId
    EntityId
    EntityRole
    Id
  AR_CacheCounters
    MetadataObjectType
    ObjectCacheCounter
    RelationshipCacheCounter
  AR_Class
    Id
    SystemId
  AR_DefaultValue
    Id
    MethodInstanceId
    TypeDescriptorId
    Value
  AR_Entity
    EstimatedInstanceCount
    Id
  AR_ExternalAssociation
    Id
    MappingTableName
    SourceEntityId
    TargetEntityId
  AR_FilterDescriptor
    Id
    MethodId
    TypeName
  AR_Identifier
    EntityId
    Id
    OrdinalNumber
    TypeName
  AR_LocalizedName
    Id
    LCID
    LocalizedName
    MetadataObjectId
  AR_MetadataObject
    Id
    IsCached
    Name
    Version
  AR_MetadataObjectSecurity
    DisplayName
    Id
    IdentityName
    MetadataObjectId
    RawSid
    Rights
  AR_Method
    ClassId
    Id
    IsStatic
  AR_MethodInstance
    Id
    MethodId
    ReturnTypeDescriptorId
    Type
  AR_Parameter
    Direction
    Id
    MethodId
    OrdinalNumber
    TypeReflectorTypeName
  AR_Property
    Id
    MetadataObjectId
    Name
    Value
  AR_System
    ConnectionFactoryTypeName
    Id
    SystemEntityTypeName
    SystemUtilityTypeName
  AR_SystemData
    Data
    Id
    Length
    Name
    SystemId
  AR_SystemInstance
    Id
    SystemId
  AR_TypeDescriptor
    ContainsFilterDescriptor
    ContainsIdentifier
    FilterDescriptorId
    Id
    IdentifierId
    InterpretedTypeName
    IsCollection
    ParameterId
    ParentTypeDescriptorId
    TypeName

A downloadable copy of the Map in PDF format is available here.