dx-doc 1:4.4.4-7 / usr / share / doc / dx / help / dxall1022

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#!CNavyBlue #!N  #!Rdatam Data 
Explorer Data Model #!N #!EC #!N #!N  #!F-adobe-times-medium-i-normal--18*   Fields #!EF are 
the fundamental informational entities in Data Explorer. A Field contains the 
components that carry the actual numbers. The "positions" component, for instance, 
contains the positions of a data set, while the "data" component 
contains the data values (e.g., temperatures). Groups are higher-level structures and 
may consist of Fields or other Groups (see  #!Lcl23,dxall1061 t Table 23  #!EL  ). #!N 
#!N Generally, a component consists of an Array of data, information 
describing the data (i.e., its type, dimensionality, or both), and a 
name associated with the component. Standard components include "positions," "data," and 
"colors." The name of a component does not usually imply anything 
about its characteristics (e.g., its data type or dimensionality). In addition, 
components typically carry attributes which indicate other characteristics of the component. 
#!N #!N For example, a "data" component should always have a 
"dep" attribute with a value of either "positions" or "connections." This 
attribute tells modules operating on the field whether the data are 
position-dependent or connection-dependent. Position-dependent data are associated one-to-one with the "positions" 
of a field, and data values can be interpolated at other 
positions in the field using the "connections" component if present. Connection-dependent 
data are associated one-to-one with the "connections" of a field, and 
data values are assumed constant within each connection. #!N #!N Another 
example of a required attribute is that the "connections" component have 
a "ref" attribute of "positions." This indicates to Data Explorer that 
the items in the connections component are to be interpreted as 
indices into the "positions" component. In addition, the "connections" component must 
have an "element type" attribute indicated the type of the connection 
(e.g. "triangles," "quads," etc.). For more information on component attributes, see 
 #!Lcompatt3,dxall223 t Table 3  #!EL  in IBM Visualization Data Explorer User's Guide. #!N #!N Module 
operations typically take place at the Field level and involve changing 
or creating components. For example: #!N #!I0 #!N  #!F-adobe-times-medium-r-normal--18*   #!N #!N 
#!I30 #!N o The Compute module may create an output Field 
whose data component is the sum of the "data" components of 
two input Fields. #!N #!I30 #!N o The AutoColor module creates 
an output Object whose "colors" component is based on the "data" 
component of the input Field. #!N #!I30 #!N o The Isosurface 
module creates an output Object whose "positions" and "connections" components describe 
a surface of constant value in the input Object's data Field. 
#!N #!I0 #!N #!EF #!N #!N #!N Modules in Data Explorer 
are generally required to be pure functions and they must not 
modify their inputs. Instead, to modify the "data" component of an 
input Object, a module must first make a copy of the 
Object. Note that the data model allows the module to copy 
the structure without copying the data. Some modules (e.g., Isosurface) create 
a completely new Object for the output (as will be illustrated 
in later chapters). #!N #!N Because a module typically works by 
manipulating the components of a Field, and because its input may 
be a more complicated Object consisting of Groups, it must often 
operate recursively. In particular, the efficient use of multiple processors requires 
that a parallel module must be able to traverse Groups, since 
partitioning creates a special type of Group called a Composite Field. 
#!N #!N For example, a module designed to add a number 
to every data value in each data component of an input 
Object first makes a copy of the input Object on which 
it is to operate. This copy duplicates the structure of the 
input Object (the hierarchy of Groups and Fields) but not the 
Arrays containing the values in the components of the Fields. In 
the worker part of the routine, a new "data" component is 
created to hold the modified data values (the other components can 
be shared with the input Object, since they will not be 
modified). #!N #!N The worker part of the routine first queries 
the Object to determine whether it is a Field or a 
Group: #!N #!I0 #!N  #!F-adobe-times-medium-r-normal--18*   #!N #!N #!I30 #!N o If 
it is a Field, the routine extracts the "data" component of 
the input Object, creates a new "data" component, places it in 
the output Object, computes the sum, puts the result in the 
new component, and returns. #!N #!I30 #!N o If it is 
a Group, the routine extracts each of the group's children and 
recursively calls itself for each child to determine whether that child 
is a Field or a Group, and so on. (See  #!Lmodexsc,dxall1027 h Working with Data  #!EL  
for an illustration of how a module performs this procedure on 
an input Object.) #!N #!I0 #!N #!EF #!N #!N #!N #!N 
 #!F-adobe-times-medium-i-normal--18*   Next Topic #!EF #!N #!N  #!Lmemng,dxall1023 h Memory Management  #!EL  #!N  #!F-adobe-times-medium-i-normal--18*   #!N