\name{P4Message-class}
\Rdversion{1.1}
\docType{class}
\alias{P4Message-class}
\alias{app,P4Message-method}
\alias{as.jlist,P4Message,list-method}
\alias{as.json,P4Message-method}
\alias{context,P4Message-method}
\alias{details,P4Message-method}
\alias{mess,P4Message-method}
\alias{sender,P4Message-method}
\alias{timestamp,P4Message-method}
\alias{uid,P4Message-method}

\title{Class \code{"P4Message"}}
\description{

  This is a message which is sent from one process to another in the
  four process architecture.  There are certain header fields with are
  used to route the message and the details field which is an arbitrary
  list of data which will can be used by the receiver.

  This class represents a semi-structured data object with certain
  header fields which can be indexed plus the free-form \code{details()}
  field which contains the body of the message.  It can be serielized in
  JSON format (using \code{\link[jsonlite]{jsonlite-package}}) or saved
  in the Mongo database (using the \code{\link[mongolite]{mongo}lite}
  package).  

}
\section{Objects from the Class}{

Objects can be created by calls to the \code{\link{P4Message}()}
function. 

}
\section{Slots}{
  \describe{
    \item{\code{_id}:}{Used for internal database ID.}
    \item{\code{app}:}{Object of class \code{"character"} which
      specifies the application in which the messages exit. }
    \item{\code{uid}:}{Object of class \code{"character"} which
      identifies the user (student). }
    \item{\code{context}:}{Object of class \code{"character"} which
      identifies the context, task, or item. }
    \item{\code{sender}:}{Object of class \code{"character"} which
      identifies the sender.  This is usually one of
      "Presentation Process", "Evidence Identification Process",
      "Evidence Accumulation Process", or "Activity Selection Process".}
    \item{\code{mess}:}{Object of class \code{"character"} a general
      title for the message context.}
    \item{\code{timestamp}:}{Object of class \code{"POSIXt"} which gives
      the time at which the message was generated.}
    \item{\code{data}:}{Object of class \code{"list"} which contains the
      data to be transmitted with the message.}
  }
}
\section{Methods}{
  \describe{
    \item{app}{\code{signature(x = "P4Message")}: returns the app field. }
    \item{as.jlist}{\code{signature(obj = "P4Message", ml = "list")}:
      coerces the object into a list to be processed by
      \code{\link[jsonlite]{toJSON}}. }
    \item{as.json}{\code{signature(x = "P4Message")}: Coerces the
      message into a JSON string. }
    \item{context}{\code{signature(x = "P4Message")}: returns the
      context field. }
    \item{details}{\code{signature(x = "P4Message")}: returns the data
      associated with the message as a list. }
    \item{mess}{\code{signature(x = "P4Message")}: returns the message field. }
    \item{sender}{\code{signature(x = "P4Message")}: returns the sender
      field.}
    \item{timestamp}{\code{signature(x = "P4Message")}: returns the timestamp. }
    \item{uid}{\code{signature(x = "P4Message")}: returns the user ID. }
  }
}
\references{

  Almond, R. G., Steinberg, L. S., and Mislevy, R.J. (2002).  Enhancing
  the design and delivery of Assessment Systems:  A Four-Process
  Architecture.  \emph{Journal of Technology, Learning, and Assessment},
  \bold{1},
  \url{http://ejournals.bc.edu/ojs/index.php/jtla/article/view/1671}. 
}
\author{ Russell G. Almond}

\seealso{
  \code{\link{P4Message}()} --- constructor
  \code{\link{parseMessage}}, \code{\link{saveRec}},
  \code{\link{getOneRec}}
}
\examples{
showClass("P4Message")
}
\keyword{classes}