here - Stefan-Marr.de

6. Evaluation: The OMOP as a Unifying Substrate
tions can be enforced by the OMOP. Reflective operations can be completely
forbidden by customizing intercession handlers for method and primitive invocation.
Mutation can be forbidden by customizing the handing of writes to
object fields, globals, and the semantics of primitives. Sec. 6.2.1 demonstrated
this by defining a ImmutableDomain.
Transactions As demonstrated with the implementation of a domain for
STM in Sec. 6.2.2, the semantics of transactions can easily be supported by
customizing the intercession handlers for reading and writing of object fields
and globals. Support for customizing the semantics of primitives completes
this support and enables full tracking of all state access and mutation operations.
6.3.2. Partially Supported Concepts
The bottom part of Tab. 6.3 covers another set of nine concepts. Their implementation
is partially facilitated by the OMOP. While they require additional
mechanisms, their implementation is simplified when they can rely on the
OMOP as a foundation.
Immutability The concepts of data streams, map/reduce, persistent data structures,
and tuple spaces all come with the implicit assumption of being used
with immutable entities. For instance, Google’s MapReduce [Lämmel, 2008]
is designed for side-effect free operators in a distributed setting. Thus, it assumes
that the data entities it operates on are immutable. The OMOP can
provide such a guarantee based on an appropriate domain definition. However,
the OMOP itself does not facilitate the execution, data handling, and
scheduling that needs to be performed by a MapReduce implementation. The
other three concepts benefit from the ability to enforce immutability in a similar
way, but a significant part of these concepts is orthogonal to the OMOP.
Thus, the OMOP provides partial support for the concept by facilitating the
implementation of a key aspect.
Ownership When it comes to the implementation of message sends, the related
concept of channels, and the general notion of by-value semantics, the
OMOP can be used to realize part of the desired guarantees. The notion of
ownership enables the distinction between sender and receiver, and for instance
enables a domain to restrict mutability, or perhaps even realize a copyon-write
notion for entities that are shared by-value. However, since message
160