31-07-2012, 11:21 AM
Data Management in Vehicle Control-Systems
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Introduction
Most functionality in modern vehicles, such as cars, is in one way or another
controlled by computers. Mechanical systems are increasingly replaced by
software residing in the vehicle control-system. As these control-systems grow
larger and larger, they become increasingly more complex to develop and maintain.
To handle this growing complexity, high-level software paradigms are
introduced, e.g., Autosar [1], a joint project within the automotive industry.
Hand in hand with the increasing amount of control functionality demanded
comes the increasing amount of information, or data, that these systems must
manage and thereby the increasing complexity of the software required. In
today’s systems, this data is handled in an ad hoc fashion, using internal data
structures, i.e., shared variables.
The current data management approach is becoming increasingly inadequate
as systems become more complex and a need for data management on a
higher level of abstraction has emerged. This problem is not unique to vehicular
systems but is, and has been, apparent in many types of computer systems
which involves managing information, such as banking and airline reservation
systems, word-processors, and e-mail/calendar applications. The solution to
data management for many of these systems has been to adopt a high-level
data management approach through the use of a database management system
(DBMS). DBMSs are used to structure data into databases, and can provide a
powerful means of access to data in a controlled fashion. This thesis investigates
how a DBMS could be introduced into vehicle control-systems.
Performing this integration is not possible without taking into consideration
the specific requirements of such a control-system. As this thesis will
Introduction
show, using a general-purpose off the shelf DBMS is not feasible. Reasons
why general purpose DBMSs are not applicable in such systems include; (i)
Traditional DBMSs are not suitable, since the onboard computers (or electronic
control units - ECUs) are too resource-constrained with respect to memory capacity.
(ii) A traditional DBMS is intended to maximize the average throughput
of data queries, while a DBMS for use in a vehicle control-system must favor
guaranteeing predictability of data accesses, such as worst case-response.
A DBMS used in a vehicle control-system must both be small enough to fit
in a small environment, and have real-time capabilities in order to provide
a time-deterministic behavior, i.e., a real-time database management system
(RTDBMS) must be used.
Problem formulation
As current DBMSs and RTDBMSs do not suit the particular requirements of
a vehicle control-system, new concepts for data management are needed. These
concepts must take the two most important aspects of embedded real-time
systems into consideration, namely; (i) Predictability with respect to timing.
The RTDBMS must guarantee that data in the database can always be accessed
within a given time. (ii) Resource efficiency with respect to memory
and CPU utilization. Since embedded systems most often have limited hardware
resources this issue has a high priority.
This thesis investigates how a data management concept for embedded realtime
systems, such as vehicle control-systems, could be designed and implemented.
In particular it will investigate the following questions:
² What are the specific data management requirements for vehicle controlsystems,
and how do these influence the characteristics of a suitable data
management concept? These requirements are used as a basis for the
development of the data management concepts performed in this work.
² How can information in an RTDBMS be accessed in a resource-efficient
and deterministic way? Introducing an RTDBMS generally increases the
computational overhead compared with using internal data structures,
therefore resource efficiency and determinism are crucial.
² How can critical and non-critical data accesses be mixed without introducing
unpredictable blocking and transaction abortions? More and
more non-critical functionality, such as multimedia services, passengercomfort,
and navigation systems, are introduced in vehicles. Accessing
1.2 The research work and method 5
non-critical data must not affect the accessing of critical data, i.e., have
a negative effect on the determinism of the system.
² How does the integration of an RTDBMS affect the data distribution in
distributed embedded real-time systems? This question is a consequence
of that most modern vehicle-control-systems are distributed among multiple
hardware nodes. For data management to be useful, it must thus
also involve data distribution.
1.2 The research work and method
The research presented in this thesis has been performed within a joint project
between M¨alardalen University, Sweden (Ph.D. student Dag Nystr¨om, Professor
Christer Norstr¨om and Associate Professor Mikael Nolin) and Link¨oping
University, Sweden (Ph.D. student Aleksandra Tesanovic and Doctor J¨orgen
Hansson). The research has been centered around a jointly developed experimental
real-time database management platform, denoted COMET RTDBMS.
The research work within the project has been divided into two separate
sections, namely, (i) data management issues for embedded real-time controlsystems
(M¨alardalen University), and (ii) reconfigurability and real-time system
development (Link¨oping University). The work and contributions presented
in this thesis describe the data management issues and concepts developed
within the COMET project.
One central aspect of the research performed within the project has been
close interaction with industry. This has enabled us to work on the solution of
research problems relevant to industrial systems in practice.
The research performed on data management for embedded real-time systems
has been conducted in three phases:
1. Investigation of the current state of the art and practices. In particular,
the current state of arts and practices in the area of embedded and
real-time database management systems has been studied [2]. An extensive
survey of commercially available embedded DBMSs was performed
and a handful of systems were investigated on the basis of a number of
criteria. In addition to this survey, a second survey was performed, this
time, of experimental RTDBMSs, developed in academia. The latter survey
also provided documentation of basic database management systems
theory.
6 Introduction
Furthermore, industrial data management requirements, assessed in a
case study performed at Volvo Construction Equipment Components
AB [3] (Paper A), provided a good foundation for continued research.
2. Formulation of initial data management concepts. Initial ideas of how
a RTDBMS could be integrated into a control-system were formulated
(Partly presented in [3] (Paper A) and further developed and concretized
in [4] (Paper B)).
3. Development and evaluation of data management concepts. In order
to make an RTDBMS suitable for use in an embedded real-time controlsystem,
several new data management concepts were needed, by; (i)
developing a number of data management concepts involving efficient
data access (Paper C), concurrency-control algorithms (Paper C & D),
and data distribution mechanisms (Paper E). In some cases, proof-ofconcept
using model-checking was performed to validate the behavior
of the proposed algorithms. (ii) implementation of the concepts, some
in our experimental platform, denoted COMET RTDBMS, and some as
test implementations. (iii) evaluation of the concepts implemented by
means of simulation
Thesis outline
The thesis is outlined as follows:
Part I:
Chapter 2 presents the areas of general purpose, real-time, and embedded
database management systems and puts these into perspective with respect
to vehicle control-systems. Related work in relevant areas is also
presented.
Chapter 3 discusses the research contributions of this work, and presents a
brief overview of the papers included.
Chapter 4 concludes the thesis and proposes some possible future directions
for continued work.
Part II:
Chapter 5-9 presents Papers A to E, which in detail discuss the different contributions
of this work.