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Appendix A: Terminology
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Appendix A: Terminology The terminology given in this book is that used in HRT-HOOD. Many of the terms are also used in HOOD, and have similar meaning. Active object an object which controls the times at which requested invocations of its operations are executed, and which may spontaneously invoke operations in other objects Budget time the time allocated to an operation or a thread for its execution Ceiling priority 2i priority assigned to all protected objects; this priority is no lower than the maximum priority of all the threads that can call the constrained operations Class an object template which represents a reusable object with type and data parameters Constrained operation an operation of an active, protected, cyclic, or sporadic object whose execution is controlled by the status of the object (as defined in the OBCS) Control flow control flow between objects is represented by the use relationship; control flow within an object is defined by the OBCS Cyclic object an object which represents a periodic activity, it may spontaneously invoke operations in other objects, but the only operations it has itself are requests which demand immediate attention (they represent asynchronous transfer of control requests) Dataflow flow of data via parameters to operations between used and using objects
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Appendix A
Deadline the time by which an operation or thread mustfinishits execution Design process tree the tree of objects of the system hting designed, consisting of the root object and its successive decomposition into child objects until terminal objects are reached Environment object an object which represents the provided interface of another object used by the system to be designed, but which is not part of the Design Process Tree Exception flow an exception is an abnormal return from a used operation to a using object Execution transformation an attribute of a cyclic or sporadic object which indicates that it must be transformed so that the thread execution has extra delays introduced Importance assigned to each cyclic and sporadic object; represents whether the thread is a hard real-time thread or a soft real-time thread Include relationship expresses that an object is fully decomposed into a set of child objects that collectively provide the same functionality as the parent Instance an object that is created for a design from a class object Internal operation an operation that is defined in a terminal object to support the implementation of provided operations Non-terminal object an object which is decomposed into child objects Object Description Skeleton - ODS the formal notation of the design of an object Object Control Structure - OBCS part of the ODS that defines the controlflowbetween constrained operations Offset an attribute of a cyclic object which indicates how long the thread must delay after creation before starting its cyclic operations Operation Control Structure - OPCS part of the ODS that defines the logic of the operation (external or internal) in terms of pseudocode
Appendix A: Terminology
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Op control object a HOOD object that implements the mapping between one parent operation and more than one child object operation OperationSet an operation which stands for a list of operations in order to ease writing of long lists of operations Passive object an object which does not have control over when invocations of its operations are executed, and does not spontaneously invoke operations in other objects Precedence constraints the constraints placed on a parent cyclic or sporadic object that its children objects must have constraints placed on their order of execution Period how often the thread in a cyclic object executes Priority the priority given to threads, according to deadline monotonic scheduling theory Protected object an object which may control when requested invocations of its operations are executed, and does not spontaneously invoke operations in other objects; in general protected objects may not have arbitrary synchronisation constraints and must be analysable for their blocking times Provided interface part of the ODS that defines tbe interface of the object Real-time attributes attributes which are given to objects to describe their real-time characteristics Required interface part of the ODS that defines the interfaces of used objects Root object the top level object which represents the system to be designed Sporadic object an object which represent a sporadic activity, it may spontaneously invoke operations in other objects; each sporadic has a single operation which is called to invoke the thread; and one or more operations which are requests demanding immediate attention (they represent asynchronous transfer of control requests) Terminal object an object which is not decomposed into child objects
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Appendix A
Thread the internal concurrent activity of a cyclic, sporadic or active object Use relationship an object is said to use another object if the former requires one or more of the operations provided by the latter Worst case execution time the maximum amount of computation time that an operation or thread requires to execute
Appendix A: Terminology The terminology given in this book is that used in HRT-HOOD. Many of the terms are also used in HOOD, and have similar meaning. Active object an object which controls the times at which requested invocations of its operations are executed, and which may spontaneously invoke operations in other objects Budget time the time allocated to an operation or a thread for its execution Ceiling priority 2i priority assigned to all protected objects; this priority is no lower than the maximum priority of all the threads that can call the constrained operations Class an object template which represents a reusable object with type and data parameters Constrained operation an operation of an active, protected, cyclic, or sporadic object whose execution is controlled by the status of the object (as defined in the OBCS) Control flow control flow between objects is represented by the use relationship; control flow within an object is defined by the OBCS Cyclic object an object which represents a periodic activity, it may spontaneously invoke operations in other objects, but the only operations it has itself are requests which demand immediate attention (they represent asynchronous transfer of control requests) Dataflow flow of data via parameters to operations between used and using objects
250
Appendix A
Deadline the time by which an operation or thread mustfinishits execution Design process tree the tree of objects of the system hting designed, consisting of the root object and its successive decomposition into child objects until terminal objects are reached Environment object an object which represents the provided interface of another object used by the system to be designed, but which is not part of the Design Process Tree Exception flow an exception is an abnormal return from a used operation to a using object Execution transformation an attribute of a cyclic or sporadic object which indicates that it must be transformed so that the thread execution has extra delays introduced Importance assigned to each cyclic and sporadic object; represents whether the thread is a hard real-time thread or a soft real-time thread Include relationship expresses that an object is fully decomposed into a set of child objects that collectively provide the same functionality as the parent Instance an object that is created for a design from a class object Internal operation an operation that is defined in a terminal object to support the implementation of provided operations Non-terminal object an object which is decomposed into child objects Object Description Skeleton - ODS the formal notation of the design of an object Object Control Structure - OBCS part of the ODS that defines the controlflowbetween constrained operations Offset an attribute of a cyclic object which indicates how long the thread must delay after creation before starting its cyclic operations Operation Control Structure - OPCS part of the ODS that defines the logic of the operation (external or internal) in terms of pseudocode
Appendix A: Terminology
251
Op control object a HOOD object that implements the mapping between one parent operation and more than one child object operation OperationSet an operation which stands for a list of operations in order to ease writing of long lists of operations Passive object an object which does not have control over when invocations of its operations are executed, and does not spontaneously invoke operations in other objects Precedence constraints the constraints placed on a parent cyclic or sporadic object that its children objects must have constraints placed on their order of execution Period how often the thread in a cyclic object executes Priority the priority given to threads, according to deadline monotonic scheduling theory Protected object an object which may control when requested invocations of its operations are executed, and does not spontaneously invoke operations in other objects; in general protected objects may not have arbitrary synchronisation constraints and must be analysable for their blocking times Provided interface part of the ODS that defines tbe interface of the object Real-time attributes attributes which are given to objects to describe their real-time characteristics Required interface part of the ODS that defines the interfaces of used objects Root object the top level object which represents the system to be designed Sporadic object an object which represent a sporadic activity, it may spontaneously invoke operations in other objects; each sporadic has a single operation which is called to invoke the thread; and one or more operations which are requests demanding immediate attention (they represent asynchronous transfer of control requests) Terminal object an object which is not decomposed into child objects
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Appendix A
Thread the internal concurrent activity of a cyclic, sporadic or active object Use relationship an object is said to use another object if the former requires one or more of the operations provided by the latter Worst case execution time the maximum amount of computation time that an operation or thread requires to execute