CONCEPTUAL FAQ

Q.I-1. What kind of data are we talking about? 
Q.I-2. How is this data stored?
Q.I-3  What is a DataSet? 
Q.I-3a. What is a RegularTimeSeries , IrregularTimeSeries or
DefaultDataSet? 
Q.I-4. What is Pathname?
Q.I-5. What is a DataReference?
Q.I-6. What is a Group?

A.I-1.
	We are primarily talking about time-series data and paired
data. In generality a (x,y) pair is one element of this data where x
is usually time and y the value.
	The corresponding class for this concept is the DataSetElement
class. It has methods for accessing the x, y and flag values for the
given element. So in other words its a collection of a x and a y and a
flag value.

A.I-2. 
	This data is stored in a database developed by HEC called
HEC-DSS. It is NOT a relational database and is specifically tuned for
fast storage and retrieval of time-series data sets. For more
information visit HEC at http://wrc-hec.usace.army.mil/. 
	HEC-DSS has a method of naming each data set ( usually time
series) with a pathname.

A.I-3
	A data set is a collection of values. Each of these values may
further consist of a x value, a y value and a flag value.
	The corresponding classes are vista.set.DataSet which then
further contains vista.set.DataSetElement.

A.I-3a.
	A regular time series is a time series that is sampled at
regular intervals and as such has the associated time window and time
interval. The corresponding class is vista.set.RegularTimeSeries
	An irregular time series is a time series that is sampled at
irregular intervals and as such has only a time window associated with
it. The corresponding class is vista.set.IrregularTimeSeries
	A paired data set is just a collection of x and y points which
are associated by some relation such as a common time stamp. The
corresponding class is vista.set.DefaultDataSet. 

A.I-4. 
	HEC-DSS stores data sets referenced by pathnames. Each unique
pathname within a file refers to a unique data set. A pathname
consists of A through F parts. A and F part are descriptive parameters
for the data set, B is the location name of the data, C is the type of
data, D is the time window and E is the time interval.
	The corresponding class for this concept is the
vista.set.Pathname class.

A.I-5.
	A data reference is a reference to a data set. It contains
information such as the filename, the pathname, the timewindow (if
any), the time interval (if any). A data reference can be either
actual data on the disk or could refer to virtual data ( data that has
resulted from a series of operations ).
	In short a data reference consists of a filename, a pathname
and a data set and optionally a server name ( if remote data ). 
	The corresponding class for this concept is the
vista.set.DataReference class.

A.I-6. 
	A Group is a group of data references. A DSS file may be
thought of as a default group that contains all the pathnames in that
DSS file.
	The corresponding class for this concept is the
vista.set.Group class.

lets recapitulate all the above concepts with this diagram

	Group --> [ DataReference0, DataReference1, ....]
	DataReference -- > [ Filename , Pathname , DataSet , Server ]
	Pathname --> [ A, B, C, D, E, F ]
	DataSet --> [ DataSetElement0, DataSetElement1, ...]
	DataSetElement --> [ x , y, flag ]

The different specialization of the above types are:


				DataReference
				     |
	-----------------------------=---------------------------
	|			     |				|
DSSDataReference	   DefaultDataReference	   MathOperationReference


				    DataSet	
					|
	--------------------------------+-----------------------
	|				|			|
IrregularTimeSeries		RegularTimeSeries	DefaultDataSet



				DataSetElement
					|
	--------------------------------+------------------------
	|		|	        	|		|
TimeElement	   TimeTuple		DefaultDataSet	      Tuple