120 research outputs found
Theory and Practice of Transactional Method Caching
Nowadays, tiered architectures are widely accepted for constructing large
scale information systems. In this context application servers often form the
bottleneck for a system's efficiency. An application server exposes an object
oriented interface consisting of set of methods which are accessed by
potentially remote clients. The idea of method caching is to store results of
read-only method invocations with respect to the application server's interface
on the client side. If the client invokes the same method with the same
arguments again, the corresponding result can be taken from the cache without
contacting the server. It has been shown that this approach can considerably
improve a real world system's efficiency.
This paper extends the concept of method caching by addressing the case where
clients wrap related method invocations in ACID transactions. Demarcating
sequences of method calls in this way is supported by many important
application server standards. In this context the paper presents an
architecture, a theory and an efficient protocol for maintaining full
transactional consistency and in particular serializability when using a method
cache on the client side. In order to create a protocol for scheduling cached
method results, the paper extends a classical transaction formalism. Based on
this extension, a recovery protocol and an optimistic serializability protocol
are derived. The latter one differs from traditional transactional cache
protocols in many essential ways. An efficiency experiment validates the
approach: Using the cache a system's performance and scalability are
considerably improved
Temporized and localized rule sets
Constraint management plays an important role in design
applications where constraints reect design restrictions and
design decisions. ECA rules are a widely used mechanism to
enforce constraints. The paper argues that such rules must be
augmented for design environments by a spatial and a temporal
dimension of validity, resulting in so-called
area-event-condition-action (AECA) rules. The spatial dimension
allows to restrict constraints locally in the design space, and
to control interaction between designers. The temporal dimension
permits designers to retract their designs to earlier stages.
The paper introduces the concept of AECA rules, motivates them
by examples from building design, discusses rule management, and
then introduces two important issues, conflict detection during
collaboration, and backtracking during design revision
Bereichsdynamische Konsistenzüberwachung
Eine Datenbankunterstützung des integrierten architektonischen
Entwurfes stellt mannigfaltige Anforderungen, die von heutigen
Datenbanksystemen nicht erfüllt werden können. Insbesondere die
Überwachung von Constraints stellt hier eine große Herausforderung
dar. Dieser Bericht hat zum Ziel, zunächst die Anforderungen an
einen Mechanismus zur Überwachung der Constraints auszuarbeiten
und anschließend ein Konzept vorzustellen, das in der Lage ist
diese Anforderungen zu erfüllen
Object-oriented protocol hierarchies for distributed workflow systems
Distributed software systems such as groupware and workflow systems
will play a key role in the near future. While numerous models which
promise highly sophisticated functionality are proposed in the
literature their implementation is still a difficult and very
expensive task. Therefore existing systems fall far behind their
promises.
Entities of the workflow level are often autonomous. Consequently,
they are related to each other in more than a fixed client/server
configuration: they often perform their activities in collaboration.
Workflow models also contain a lot of information about the system\u27s
dynamics. If one uses objects as an implementation mode
Multi-object cooperation in distributed object bases
It is an emerging trend to build large information systems in a
component-based fashion where the components follow the concept of
object. Applications are constructed by organizing pre-built objects
such that they cooperate with each other to perform some task.
However, considerable programming effort is required to express
multi-object constraints in terms of the traditional message-passing
mechanism. This observation lead many authors to suggest
communication abstractions in object models. One promising approach
is to separate multi-object constraints from the objects and collect
them into a separate construct. We call this construct an alliance.
Unlike other approaches we allow alliances to involve large sets of
long-lived objects which may dynamically vary during the - also
potentially long - life-time of the alliance. Alliances are not only
visible at the specification level but are also computational
entities which enforce multi-object constraints at run-time.
They do so in an unreliable world, i.e., we do not assume that
objects will always meet their obligations in a cooperation.
Since objects may often be distributed across a network, we
demonstrate that alliances are an ideal place to deal with aspects
of distribution in an application-specific manner. We illustrate our
thesis by one of the key questions of distributed object management:
where shall objects be located and when shall they migrate to which
node? We show that alliances allow for customized distribution
policies which are neither "hardwired" into the objects nor
necessitate a centralized distribution control
Modulare Aufbereitung von multimedialen Lerninhalten für eine heterogene Lernumgebung
Der Einsatz multimedialer Lerninhalte ist durch die vielfältig
vorhandenen und sich ständig verbessernden technischen
Möglichkeiten ein aktuell weit verbreitetes Thema. Ihre
Erstellung gestaltet sich allerdings äußerst aufwendig. Daher
beschäftigen wir uns mit der kooperativen Entwicklung von
multimedialen Lehr-/Lerninhalten, die von verscheidenen Autoren
in unterschiedlichen Kontexten für verschiedene Zielgruppen
eingesetzt werden können. Unser Ansatz basiert auf dem
Modularisierungskonzept zur Unterstützung der
Wiederverwendbarkeit von Lernmaterialien. Um solche
"universellen" Lernmodule zu entwickeln, die sowohl die
Bedürfnisse verschiedener Zielgruppen als auch verschiedener
Autoren erfüllen, werden mehrere Modularisierungsebenen
eingeführt und die Erzeugung verschiedener Modulsichten
ermöglicht
Konsistenzüberwachung in Datenbanksystemen - Eine Anforderungsanalyse anhand der Entwurfsbereiche Architektur und Schiffbau
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