Differences Between UNO and Corba

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This subsection discusses the differences between UNO and CORBA by providing the fundamental differences and if the different concepts could be mapped into the world of the other model. Consider the following feature comparison. The column titled "Mapping possible" states if a feature could be mapped by a (yet to be developed) generic bridge.

UNO CORBA Mapping possible
multiple inheritance of interfaces no yes yes
inheritance of structs yes no yes
inheritance of exceptions yes no yes
mandatory base interface for all interfaces yes no yes
mandatory base exception for all exceptions yes no yes
context of methods no yes no
char no yes yes
8 bit string no yes yes
array no yes yes
union no yes yes
assigned values for enum yes no yes
meta type 'type' yes no yes
object identity yes no no
lifetime mechanism yes no no
succession of oneway calls yes no no
in process communication yes no no
thread identity yes no no
customized calls no yes yes
less code generation yes no no
  • Multiple Inheritance
CORBA supports multiple inheritance of interfaces, whereas UNO only supports single inheritance.
Mapping: Generates an additional interface with all methods and attributes of the inherited interfaces that must be implemented in addition to the other interfaces.
  • Inheritance of Structs
In contrast to CORBA, UNO supports inheritance of struct types. This is useful to define general types and more detailed subtypes.
Mapping: Generate a struct with all members, plus all members of the inherited structs.
  • Inheritance of Exceptions
CORBA does not support inheritance for exceptions, whereas UNO does. Inheritance of exceptions allows the specification of a complex exception concept. It is possible to make fine granular concepts using the detailed exceptions in the layer where they are useful and the base exception in higher levels. The UNO error handling is based on exceptions and with inheritance of exceptions it is possible to specify 'error classes' with a base exception and more detailed errors of the same 'error class' that inherit from this base exception. On higher level APIs it is enough to declare the base exception to specify the 'error class' and it is possible to support all errors of this 'error class'.
Mapping: Generates an exception with all members, plus all members of the inherited exceptions. This is the same solution as for structs.
  • Mandatory Base Interfaces
UNO specifies a mandatory base interface for all interfaces. This interface provides acquire() and release() functions for reference counting. The minimum life time of an object is managed by means of reference counting.
  • Mandatory Base Exception
UNO specifies a mandatory base exception for all exceptions. This base exception contains a string member Message that describes the reason for the exception in readable format. The base exception makes it also possible to catch all UNO exceptions separately.
  • Method Context
CORBA supports a request context. This context consists of a name-value pair which is specified for methods in UNOIDL. The context is used for describing the current state of the caller object. A request context provides additional, operation-specific information that may affect the performance of a request.
  • Type char
UNO does not support 8-bit characters. In UNO, char represents a 16-bit unicode character.Mapping: To support 8-bit characters it is possible to expand the TypeClass enum to support 8-bit characters and strings. The internal representation does not change anything, the TypeClass is only relevant for mapping.
  • 8 bit string
UNO does not support 8-bit strings. In UNO, string represents a 16-bit unicode string.
Mapping: The same possibility as for char.
  • Type array
UNO does not support arrays at the moment, but is planned for the future.
  • Type union
UNO does not support unions at the moment, but is planned for the future.
  • Assigned Values for enums
UNO supports the assignment of values for enum values in IDL. This means that it is possible to use these values directly to specify or operate with the required enum value in target languages supporting this feature, for example, . C, C++.
Mapping: Possible by using the names of the values.
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