L-DALI User Manual
110
LOYTEC
Version 5.2
LOYTEC electronics GmbH
6 Concepts
6.1 Data Points
6.1.1 Overview
Data points are part of the fundamental device concept to model process data. A data point
is the basic input/output element on the device. Each data point has a value, a data type, a
direction, and a set of meta-data describing the value in a semantic context. Each data point
also has a name and a description. The entire set of data points is organized in a hierarchy.
At the data point level, the specific technological restrictions are abstracted and hidden from
the user. Working with different technologies at this level involves common work-flows for
all supported technologies.
The direction of a data point is defined as the “network view” of the data flow. This means,
an input data point obtains data from the network. An output data point sends data to the
network. This is an important convention to remember as different technologies may define
other direction semantics. If a data point can both receive and send data on the network, its
direction is set to value, indicating no explicit network data flow.
The basic classes of data points are:
Analog
: An
analog
data point typically represents a scalar value. The associated data
type is a
double precision
machine variable. Meta-data for analog data points include
information such as value range, engineering units, precision, and resolution.
Binary
: A
binary
data point contains a Boolean value. Meta-data for binary data points
includes human-readable labels for the Boolean states (i.e., active and inactive texts).
Multi-state
: A
multi-state
data point represents a discrete set of states. The associated
data type is a signed integer machine variable. Each state is identified by an integer
value, the
state ID
. State IDs need not be consecutive. Meta-data of a multi-state data
point includes human-readable descriptions for the individual states (state texts) and the
number of available states.
String
: A
string
data point contains a variable-length string. The associated data type is
a character string. International character sets are encoded in UTF-8. A string data
point does not include any other meta-data.
User
: A
user
data points contains un-interpreted, user-defined data. The data is stored
as a byte array. A user data point does not include any other meta-data. This type of
data point also serves as a container for otherwise structured data points and represents
the entirety of the structure.
