Cost-Based Optimization of Integration Flows - Datenbanken ...

2.1 Integration Flows
complex queries, Publish/Subscribe systems usually execute huge numbers of fairly simple
queries. On the other side, there are ETL tools that follow a time-based or data-driven
event model. All three system categories conceptually use a hub-and-spoke or bus topology,
where in both cases a central integration platform is used. Finally, all system types
of the application area of information integration are query-based in the sense of the specification
method for integration task modeling. A special case is given by ETL tools that
often use integration flows as the specification method as well.
The categories of application integration and process integration refer to a more loosely
coupled type of integration, where integration flows are used as specification method and
message-oriented flows are hierarchically composed. The main distinction between both
is that application integration refers to the integration of heterogeneous systems and applications,
while process integration refers to a business-process-oriented integration of
homogeneous services (e.g., Web services). Thus, both are classified as materialized integration
approaches because messages are propagated and physically stored by the target
systems. However, application integration is data-centric in terms of efficiently exchanging
data between the involved applications, while process integration is more focused on
procedural aspects in the sense of controlling the overall business process and its involved
systems. In this context, we see many different facets of system types such as (near)
real-time ETL tools (that use the data-driven event model), MOM systems (that use
standard-messaging infrastructures such as Java Message Service), EAI systems, BPEL
Engines (Business Process Execution Language), and Web Service Management Systems
(WSMS). Note that those system categories have converged more and more in the past
[Sto02, HAB + 05] in the form of overlapping functionalities [Sto02]. For example, standards
from the area of process integration such as BPEL are also partially used to specify
application integration tasks.
Finally, GUI integration (Graphical User Interface) describes the unique and integrated
visualization of (or the access to) heterogeneous and distributed data sources. Portals
provide a unique system for accessing heterogeneous data sources and applications, where
data is only integrated for visualization purposes. In contrast, mashups dynamically compose
Web content (feeds, maps, etc.) for creating small applications with a stronger focus
on content integration. See the classification by Aumueller and Thor [AT08] for a detailed
classification of existing mashup approaches. Both portals and mashups are classified as
virtual integration approaches that use a hierarchical topology, and the specification is
mainly user-interface-oriented.
The exclusive scope of this thesis is the category of integration flows. As a result, the
proposed approaches can be applied for process integration, application integration, and
partially information integration as well.
2.1.2 System Architecture for Integration Flows
The integration of highly heterogeneous systems and applications that require fairly complex
procedural aspects makes it almost impossible to realize these integration tasks using
traditional techniques from the area of distributed query processing [Kos00] or replication
techniques [CCA08, PGVA08]. In consequence, those complex integration tasks are
typically modeled and executed as imperative integration flow specifications.
Based on the specific characteristics of integration flows, a typical system architecture
has evolved in the past. This architecture is commonly used by the major EAI products
such as SAP eXchange Infrastructure (XI) / Process Integration (PI) [SAP10], IBM
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