current, e.g. a customer cancelling their subscription
to a particular service which effectively implies that
the customer never had a relationship with the
company. In contrast, historical databases do not
delete records (without administrator intervention)
and only update and insert new records in order to
maintain an object’s historical audit trail. This
supports data mining and the recognition of trends as
results of object states and aggregate statistics can be
compared at different time points.
Temporal databases manage time values in one
of two ways: i) valid time and ii) transaction time.
Valid time denotes the time period during which a
fact is true with respect to the real world.
Transaction time is the time period during which a
fact is stored in the database. Some databases also
support a bi-temporal mode by including both valid
time and transaction time support.
In terms of building information, a temporal
database could be used, for example, to record
temperature changes within defined spaces. By
assigning a ‘start’ and ‘end’ (valid time) timestamp
to each record, it is possible to develop a complete
history of temperature fluctuations in different
rooms, and these records could be searched in order
to find the temperature of a given room at any past
point in time, or used to find the average
temperature during a period of time. This is one,
fairly simplistic example, however, the potential to
creating temporal relationships gives rise to much
more advanced functionality, including the ability to
support mobile sensors. If sensors in a building were
able to move between spaces, their readings could be
linked to the correct space objects. In this instance it
would be possible for the sensor to create records for
each temperature reading, but for each reading to be
attributed to the correct room. As a result of the
potential to create temporary relationships between
objects, and track the full history of all object
interactions, IB software would be provided with a
wealth of knowledge that could be mined to
recognise patterns to support resource efficiency and
user well-being optimisation.
There are, however, several difficulties to be
overcome in the development of a temporal database
based IB model, including: the complexity of design,
implementation and mining of data, as well as the
potential performance problems due to the complex
requirements of managing records. Perhaps the
greatest obstacle to the adoption of temporal
databases, however, is the lack of support from
database vendors.
Whilst some vendors, particularly Oracle, have
recently made efforts to include temporal features
into their database products, no single product
supports all the required features which are required
for a true temporal database. As a result the
management and querying of temporal data is still a
cumbersome and complex process due to the lack of
supported temporal features in existing RDBMS
(Relational Database Management System)
products. This state of affairs is due, at least in part,
to the exclusion of temporal features from the SQL
ISO standard.
In addition to the technical difficulties, there are
also social obstacles to be overcome, especially
when attempting to use such a database for the
purpose of tracking and recording occupant
behaviour, as such a system threatens damaging the
trust relationship between staff and management.
Moran et al. (2010) investigated this problem and
provided suggestions as to how organisations should
deal with the issues including: how data is collected
and for what purpose, access rights to the data and
the length of time temporal data is held by the
organisation.
4 PROTOTYPE OF THE
PROPOSED SOLUTION
In response to the need for a dynamic building
model standard, we propose the use of an adaptive
building model based on IFC and temporal
databases. The IFC model is capable of providing a
complete, yet static, representation of a building’s
structure and content, whilst the temporal database
will handle the recording, management and retrieval
of all object state changes. Figure 1 shows a diagram
of the proposed solution including the relationship
and differences between the proposed building
model and the currently available BMS technology.
A prototype system was developed using object-
oriented technology in order to support a continuous
simulation of the building, where each item has a
corresponding software object. Any change to these
objects, as reported by building sensors, is
immediately updated in the run-time software
objects and the related database records. The current
version of the prototype focuses on the simulation of
sensor instances linked to spaces and supports the
recording of sensor readings in a temporal database
as well as the visualisation of these readings.
For the sake of simplicity, the prototype
currently supports a variable number of temperature
sensors that can be set to create a new reading every
n number of seconds for a specified time period. The
readings are recorded in a temporal database that can
be visualised with a simple web-based interface. The
simulation was developed using an open-source
platform including linux, Java and MySQL. The
visualisation was developed with Apache, PHP and
INCLUSION OF TEMPORAL DATABASES WITH INDUSTRY FOUNDATION CLASSES - A Basis for Adaptable
Intelligent Buildings
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