mtaskext.sdssem.tex

   1 \Gls{mTask}-\glspl{SDS} on a client are available on the server as in the form
   2 of regular \gls{iTasks}-\glspl{SDS}. However, the same freedom that an
   3 \gls{SDS} has in the \gls{iTasks}-system is not given for \glspl{SDS} that
   4 reside on the client. Not all types are suitable to be located on a client,
   5 simply because it needs to be representable on clients. Moreover, \glspl{SDS}
   6 behave a little different in an \gls{mTask} device compared to in the
   7 \gls{iTasks} system. In an \gls{iTasks} system, when the \gls{SDS} is updated,
   8 a broadcast to all watching \glspl{Task} in the system is made to notify them
   9 of the update. \glspl{SDS} can update often and the update might not be the
  10 final value it will get. Implementing the same functionality on the \gls{mTask}
  11 client would result in a lot of expensive unneeded bandwidth usage. Therefore
  12 a device must publish the \gls{SDS} explicitly to save bandwidth. Note that
  13 this means that the \gls{SDS} value on the device can be different compared to
  14 the value of the same \gls{SDS} on the server.
  15
  16 To add this functionality, the \CI{sds} class could be extended. However, this
  17 would result in having to update all existing views that use the \CI{sds}
  18 class. Therefore, an extra class is added that contains the extra
  19 functionality. Programmers can choose to implement it for existing views in the
  20 future but are not obliged to. The publication function has the following
  21 signature:
  22 \begin{lstlisting}[caption={The \texttt{sdspub} class}]
  23 class sdspub v where
  24   pub :: (v t Upd) -> v t Expr | type t
  25 \end{lstlisting}
  26
  27 Moreover, \glspl{SDS} in the \gls{mTask}-\gls{EDSL} are always anonymous. There
  28 is no way of labeling it since it is not a real entity, it is just a function.
  29 When a \gls{SDS} is sent to the device it must be retrievable and identifiable.
  30 It is not always clear which instantiated \gls{SDS} is which. Therefore, an
  31 added class named \CI{namedsds} is added that provides the exact same
  32 functionality as the \gls{SDS} class but adds a \CI{String} parameter that can
  33 later be used to identify a \gls{SDS}. The types for this class are as follows:
  34
  35 \begin{lstlisting}[caption={The \texttt{namedsds} class}]
  36 class namedsds v where
  37   namedsds :: ((v t Upd)->In (Named t String) (Main (v c s))) -> (Main (v c s)) | type, mTaskType, toCode t
  38 :: Named a b = Named infix 1 a b
  39 \end{lstlisting}