\name{getAnnMap}
\alias{getAnnMap}

\title{Get annotation map}
\description{
  This function retrieves a map object from an annotation data
  package.  It is intended to serve as a common interface for
  obtaining map objects from both SQLite-based and environment-based
  annotation data packages.
}
\usage{
getAnnMap(map, chip, load = TRUE, type = c("db", "env"))
}

\arguments{
  \item{map}{a string specifying the name of the map to retrieve.  For
      example, \code{"ENTREZID"} or \code{"GO"}}
  \item{chip}{a string describing the chip or genome}
  \item{load}{a logical value.  When \code{TRUE}, \code{getAnnMap}
      will try to load the annotation data package if it is not
      already attached.}
  \item{type}{a character vector of one or more annotation data
      package types.  The currently supported types are \code{"db"} and
      \code{"env"}.  If \code{load} is \code{TRUE}, you can specify both
      \code{"db"} and \code{"env"} and the order will determine which
      type is tried first.  This provides a fall-back mechanism when the
      preferred annotation data package type is not available.  If
      \code{type} is missing, then the first matching annotation package
      found in the search path will be used, and then the default value
      of \code{type} takes over.}
}
\details{
  \code{getAnnMap} uses the search path (see \code{search}) to find an
  appropriate annotation data package; when called with
  \code{chip="hgu95av2"}, the function will use the first hgu95av2
  package on the search path whether it be db or environment-based.  If
  \code{load=TRUE} and no suitable package is found on the search path,
  then the function will attempt to load an appropriate package.  The
  \code{type} argument is used to determine which type of package (db or
  env) is loaded first.
}
\value{
  If \code{type} is \code{"db"}, an S4 object representing the
  requested map.  If \code{type} is \code{"env"}, an R
  \code{environment} object representing the requested map.
}

\author{Seth Falcon}

\examples{
map <- getAnnMap("ENTREZID", "hgu95av2", load=TRUE, type=c("env", "db"))
class(map)
}

\keyword{manip}