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CNKBuf,

CNKBufReader,

CNKBufWriter:

Data Buffers

The three classes CNKBuf, CNKBufReader, and CNKBufWriter together

are used to implement a first-in-first-out (FIFO) data buffer containing

multiple rows, where each row contains multiple columns of data.

The different columns can contain data of different types.

CNKBuf object contains the actual data in the buffer. In addition, it

contains information about the number and types of the columns.

CNKBuf has methods for accessing the column type information, such

as the list of level strings for a given factor column.

CNKBufReader and CNKBufWriter objects are used to read or write the

data within a

CNKBuf. These objects are used, rather than accessing

the

CNKBuf directly, because there may be multiple CNKProc objects

reading a given

CNKBuf at a time. Each of the CNKBufReader objects

represents a connection between a particular

CNKBuf and a particular

CNKProc. The same mechanism is used for writing to a CNKBuf, even

though currently only one

CNKBufWriter can write to a given CNKBuf.

CNKBufReader and CNKBufWriter objects cannot be created

independent of a

CNKBuf or CNKProc. They are created by passing a

CNKBuf object to the CNKProc::setInputBuf or

CNKProc::setOutputBuf methods, which creates the appropriate

CNKBufReader or CNKBufWriter object, and establishes the

connections between the

CNKBufReader (or CNKBufWriter), the

CNKProc, and the CNKProc objects. When a CNKBuf or CNKProc object

is deleted, these connections are automatically removed.

The

CNKBuf class is the heart of the pipeline architecture. The design

of the data-manipulation components (in the

CNKProc class) is very

simple, to make it as easy as possible to create new components.

CNKBuf objects, used to coordinate data flow between CNKProc objects,

are somewhat more complicated. A

CNKProc component must follow

certain rules when accessing a

CNKBuf object, in order for this

coordination to work. Loosely speaking, a

CNKBuf can be viewed as a

first-in-first-out (FIFO) buffer of data rows. One

CNKProc can write a

series of data rows into the

CNKBuf (using a CNKBufWriter object), and

one or more other

CNKProc objects can read out these data rows in the

same order (using

CNKBufReader objects). Things are a bit more

complicated, because (1) a given

CNKBuf has a limited size, so it can

only store a certain number of written data rows at a time, and (2) the

pipeline architecture is designed so that all

CNKBuf methods return

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