|
|
|
Student Projects
Students are welcome to contribute to the research project either as
paid student researches or with Project, Diploma, Bachelor or
Master thesis. There are the following student projects:
| Topic |
Propagation of ECSL Cardinality Constraints with Respect to CEP Queries |
| State |
Finished |
| Student research and Bachelor thesis of |
Thanh Son Dang |
| Time period |
February - December 2011 |
| Abstract |
Semantic optimization of database queries, i.e. the use of metadata (constraints) for query optimization,
is well investigated and has led to significant performance gains. The algorithm semantically rewriting
database queries is applicable to CEP queries with some adaptions. One of these adaptions concerns the
treatment of views and the constraints for them.
To reduce the number of constraints which must be manually specified by the user, the algorithm semantically
rewriting database queries leads views back to their respective base relations so that constraints have to be
defined for base relations only. However, if a CEP engine involves automatic garbage collection of events and
states, the relations saving these events and states may become incomplete in the meantime such that CEP views
cannot be led back to them without lost of tuples in some cases. Therefore, an approach opposite to the one in
databases is introduced in this work: ESCL cardinality constraints are automatically propagated from base events
(states) to the derived events (states) with respect to the queries deriving them, i.e. only the ESCL cardinality
constraints for base events and states must be manually specified by the user. The propagation of the other kinds
of ESCL constraints is to be investigated.
The approach presented in this report is independent from an event query language. To illustrate it, CEP queries
are expressed in StreamLog, a first order logic language extended with temporal aspects as required for CEP.
|
| Goals |
- Algorithm propagating ESCL cardinality constraints with respect to StreamLog queries independently from
the complexity of queries and constraints, query evaluation time must not coincide with constraint validity time
- Proofs of termination, correctness, and completeness of the algorithm, investigation of its complexity
|
| Topic |
Instantiating Hierarchical Timed Automata |
| State |
Finished |
| Project thesis of |
Sandro Giessl |
| Time period |
November 2010 - May 2011 |
| Abstract |
The application logic of many information systems often follows a given workflow enforcing certain
orders and dependencies of events. This knowledge can be used to make event processing more efficient.
To this end Instantiating Hierarchical Timed Automata (IHTA) capturing the knowledge are formally
defined in this work. Later, constraints will be derived from IHTA and used by the semantic query
optimisation algorithm.
IHTA are nondeterministic automata the states of which correspond to the application states and
the edges between them are labeled with event queries and temporal constraints.
The labels of IHTA are more expressive than that of Timed Automata for the following reasons.
First, the event queries of IHTA allow access to event data.
Second, the temporal constraints of IHTA are expressed on the beginning and the end of the occurrence
time of matched events (and not on local clocks).
Each state of IHTA is either atomic or non-atomic, i.e. is IHTA itself, so that an arbitrary level
of abstraction can be reached. The idea of a hierarchy of models is not new. Hierarchical Timed Automata
and Statecharts are examples of such models. However, only a fixed number of concurrent processes
can be modelled by them. IHTA extend them by instantiation allowing an arbitrary number of
concurrent processes (specified by the same non-atomic state) to run at the same time.
|
| Goals |
- Requirements to a model of application semantics of event-based systems
- Analysis of automata, flowcharts, Petri nets, and UML with respect to these requirements
- Syntax and semantics of IHTA, automaton configuration modification
|
|
|
|