1 Introduction Synchronization in Multimedia Languages for Distributed Systems

Synchronization in Multimedia Languages for Distributed Systems

A. Guercio1, A. Bansal2, T. Arndt3

1Department of Mathematical Sciences, Kent State University

2Department of Computer Science, Kent State University

3Department of Computer and Information Science, Cleveland State University

1 Introduction

The rising popularity of multimedia content on the web has led to the development of special-purpose languages for multimedia authoring and presentations. Examples of such languages include SMIL [1], VRML [2], and MPEG4 [3]. These languages support the description of a multimedia presentation containing multiple media sources including both natural and synthetic media as well as media stored in files or streamed live over the network. Some mechanism for specifying the layout of the media on the screen is given as well as a set of primitives for synchronizing the various elements of the presentation. For example, in SMIL we can specify that two video clips be displayed in parallel or that one audio clip be started when another clip finishes. Some of these languages allow for a limited amount of user interactions. A SMIL 2.0 presentation might allow a user to choose a soundtrack in one of several different languages by clicking on a particular area of the presentation. This is accomplished through the incorporation of the events defined in a scripting language such as JavaScript.

While these are well suited for the description of multimedia presentations on the Web, they are of limited use for creating more general distributed multimedia applications since general-purpose programming is only available in the form of scripting languages that have limited power. To support the construction of more large-scale applications approaches such as the use of special multimedia libraries along with a general-purpose language as in the case of Java and JMF [4] or the extension of middleware such as Corba [5] have been proposed. Besides lacking certain essential characteristics for the development of advanced distributed multimedia applications that will be noted below, the use of libraries and/or middleware to achieve synchronization and perform other media related services results in a less well-specified approach than can be achieved by directly extending existing general purpose languages with multimedia constructs with precisely specified semantics. This latter is the approach we follow in our work on multimedia languages that we will describe here.

The language that we want to design should support general-purpose computation; therefore the multimedia constructs whose semantics we will describe should be added to an existing general purpose language such as C, C++ or Java. This is the approach taken by the reactive language Esterel [6]. Reactivity is a very important property for a multimedia language. A reactive system is one which responds to stimuli from the environment [7]. In a multimedia system such stimuli might include user interactions as well as (for example) events generated by the contents of some media stream. The multimedia system must be able to interact with the environment within a short, predefined time period. When used in this context, the difference between reactive systems and interactive systems is that while both may interact with the environment, the latter do not have such a time constraint. The way in which the environment interacts with the multimedia system is through the generation of signals. A signal can be either synchronous (e.g. the reading of some sensing device) or asynchronous (e.g. the recognition of a particular face in a video stream). Our approach to multimedia languages greatly increases the power and flexibility of synchronization by providing synchronization constructs which can be applied not just between media streams, but also between media streams and (synchronous or asynchronous) signals. In fact, in our approach multimedia streams are just a particular type of signal.

The rest of this paper is organized as follows. Section 2 describes the fundamental concepts of signals and streams. Section 3 introduces the various synchronization mechanisms. Section 4 describes the language constructs. Section 5 discusses related research while section 6 describes future research.

2 Signals and Streams

Reactive systems respond to signals generated by the environment. The response must occur within a predefined time period. The signals may have a value. They may also be either periodic or aperiodic. An example of a periodic signal is one which might be generated by a sensor, like a thermometer, which periodically sends the temperature in the form of a signal to the reactive system. An example of an aperiodic signal might be the coordinate values generated by a user using a mouse which are generated only when the user moves the mouse. In order to generalize synchronization of multimedia streams, we define a multimedia stream as a particular type of signal. This allows us to apply the synchronization constructs not just to multimedia streams but to streams and other signals as well.

Reactive multimedia systems often transform or respond to multimedia data which is coming from a

sensor such as a digital video camera. The sensor discretizes the continuous media data, converting it into a periodic stream. In such a stream, the multimedia data is associated with a periodic signal. Other types of interactions can produce an aperiodic stream. An example might be a security camera which transmits an image only when motion is detected along a fence line. We model these streams, both periodic and aperiodic as a pair of data and attributes where the data is a sequence of tuples whose elements can be either (elementary) values or tuples. Since multimedia streams are directly associated with a signal, we use the words “stream” and “signal”interchangeably. Formally, we define three types of streams, periodic, continuous and aperiodic, as follows. Definition 1: A periodic stream S P is a sequence of elements associated with periodic signals. S P i is the i-th element in the sequence such that the period p does not vary, that is the time between S P(i+1) and S P i is the same as the time between S P(j+1) and S P j, ?i,j with i≠j.

Definition 2: A continuous stream is the data produced continuously by a sensor. A sensor is used to detect information from the environment. A continuous stream can be modeled as a periodic stream with periodicity 0 < p < εwhere εis a small value. The period p represents the rate at which the signal is produced.

Definition 3: An aperiodic signal can be generated at any time either by an external stimulus or by an event generated after a computation or through a user interaction (such as voice or mouse movement). An aperiodic stream S A is a sequence (possibly of length one) of aperiodic signals. In an aperiodic stream S A i represents the i th aperiodic signal.

A multimedia stream is then defined as follows. Definition 4:A multimedia stream S has two components: attribute-set and data. Three attributes periodic or aperiodic, number of data elements per unit time, and type of data (such as audio or video or music or audiovisual etsc.) are essential. Other attributes are specific to the streams, and vary with different types of multimedia streams.

Let us consider an example of a multimedia stream. Example 1: A quadraphonic audio stream is a continuous periodic multimedia stream, whose components are:

(i) the data represented as a sequence of sampled packets;

(ii) the attribute-set A={a0 = periodic, a1= audio,

a2= 44,100 samples per second, a3= no. of

channels = 4, a4 = 16 bits per sample, a5 = media

length, …}.

As an example of an aperiodic stream we have the following.

Example 2: Aperiodic signals have data and attributes as well. An example of an aperiodic signal is m o u s e movement. The components of this aperiodic signal are: (i) the data which describes the mouse movement as a sequence of (X-coordinate, Y-coordinate);

(ii) the attribute-set A={a0= aperiodic, a1=“Mouse Movement”, …}.

3 Synchronization

Multimedia synchronization represents some logical relationship (temporal, spatial, spatiotemporal, or logical) between two or more multimedia streams or objects [8]. In the context of research in multimedia computing, however, it is customary to use synchronization to describe only the temporal relationship [9]. Synchronization can also mean intra-media synchronization, which defines the temporal constraints within a single multimedia stream; however in general synchronization means inter-media synchronization.

Synchronization research can be done on a number of issues [8]. Among these are modeling and specification of synchronization requirements, synchronization algorithms and protocols, and fault recovery in the presence of failures. Our research falls in the first category.

In order for multiple streams to be synchronized, they must share a common clock. In centralized systems it is possible for all streams to use the same physical clock, but this is not possible in distributed systems. The use of multiple physical clocks in such systems is problematic since clock drift can cause skew between the clocks. In order to control this, the multimedia data source insert synchronization points into the streams. The synchronization points can be media points or event counters which preserve the partial ordering of events [10]. In general, inserting more sync points allows for a finer degree of synchronization, but with the cost of added overhead. For synchronization purposes, the multimedia streams need to share a common clock (possibly a logical clock). This common clock provides a common time-base used for synchronization purposes [11].

One of the issues we should take into account while synchronizing media streams is the possibility to have synchronization skew. For example, for good lip synchronization the limit of the synch skew is ±80 msec between audio and video. In general, ±200 msec is still acceptable. For a video with speaker and voice the limit is 120 msec if the video precedes the voice and 20 msec if the voice precedes the video [Li04]. The worst sync skew that can occur depends on how far apart the synch points have been chosen. The closer the synch points, the more resources (such as buffer space) are required when the system is running but more precision in synchronization will be obtained. How should the synch points be chosen if we have several streams with different synch points to be synchronized? Of course, a common synch point for all the streams must be found. If do not need a very strict synchronization or we want to save resources, we

explicitly define the synch points to be further apart. For example, if two streams are dependent and one stream has sync points every 2 seconds and the other stream every 3 seconds, a resource saving choice would be to select as the common sync point the least common denominator of the two synch points, i.e. 6 seconds. However, it is highly probable that this choice would not provide great results from the visualization point of view, since it would increase the chance of perceptual distortion. Therefore, this choice is not appropriate in our case where synchronization must be very tight. A more restrictive option is used by selecting the smallest of the values of the synch points of the streams.

3.1 Groups

A distributed multimedia system receives input data from sources, which can be either local or remote. The input data are either streams of media data or asynchronous signals produced by the interaction of the system with the external environment. Because of the temporality of the input data involved in the model, each multimedia stream S generated from the source has an associated clock c∈ C and forms a multimedia source Src(S, c). Many streams can be generated at the same instant from different sources. Some of these streams must be treated by the distributed reactive multimedia systems as dependent on one another; other streams must be treated independently. For example, suppose that an audio and a video are produced from two distinct sources and that they must be rendered at the same time. If we later decide to speed up one of the two streams what should happen to the second one? If they are dependent the second should speed up as well, on the other hand if they are independent, the second one should proceed undisturbed. We show the dependence of the streams by defining them to be members of the same group. Definition 5: A group G is defined recursively as:

(i) A single multimedia stream such that the time-

base of G is same as the time-base of the

stream.

(ii)Two or more multimedia streams sharing a

common time base or with their time-bases

related through an equation for proper

synchronization.

Logically, a group is a tree in which the interior nodes of the tree are groups, and the leaf nodes are multimedia streams. Groups express of dependency of streams and operations performed on the group will influence all of the elements of the group. Operations on a particular multimedia stream of a group (e.g. scaling of the time-base) can either be applied in isolation or to all of the streams in a group to which the stream belongs. We will call the first type of operation isolated and the second type synchronized.3.2 The Synchronization Process

The synchronization process consists of a set of spatio-temporal functionalities that enables rendering of multimedia objects in multiple streams to have the same perception as if it happened in real time. Inter-media synchronization involving multiple media streams requires the ability to relate the clock of each stream either through a common shared time-base or through an equation relating the two time-bases. If two multimedia streams are grouped together (are dependent) then changing the time-base of one stream similarly affects the time-base of the other stream to maintain synchronization. Definition 6: Given n streams S1, S2,…, S n, in a multimedia group G={S j, S j+1,…, S m}, a n d a synchronization function f, the application f(S i) (1 ≤ i ≤ n) enforces the application of function f on all the multimedia streams S1, S2, …, S n such that the synchronization constraint is maintained.

Consider the lip synching of an audio and a video stream that are played in a lock step manner to give a realistic perception. The two streams are grouped so that time-scaling on either stream (e.g. time stretching or compressing the video) causes the other stream to be time-scaled to maintain synchronization.

The grouping of streams is dynamic and event-driven. That is, certain events may affect a group in one way while another event may affect the group in another way. This dynamic behavior can be obtained either by having multiple orthogonal groups and associating different events with different groups, or by dynamically ungrouping and regrouping the streams through language grouping constructs.

4 Language Constructs

In this section we will describe those language constructs that support synchronization in reactive multimedia systems. Due to space limitations, we are not able to give all of the language constructs. The exact syntax of the constructs will depend on the host language that the multimedia constructs are embedded in.

4.1 Stream Definition

Declarations of media streams are given in terms of the source of the stream (a URL) and the type of the stream (audio, video, audiovisual, etc.) An asynchronous stream can be defined as well. The granularity of the sync points is given as well. Each different type of multimedia stream has a number of attributes whose values are given as part of the declaration (e.g. audio attributes include the name of the stream, number of samples per second, number of channels, number of bits per sample, etc.).

Example 3:The following code is used to declare and initialize an audio stream coming from a remote source. The file name is “speech.mov” and the origin of the media is indicated by the URI address of the source. The audio received can be rendered in the systems at 44,100 samples/sec with 16 bits/sample over 2 channels and the playback rate should not be slower than half of the normal rate, nor more than twice as fast as the normal rate. The stream should have a sync point every 200 milliseconds. The host language is C.

audio_stream mm1={source1, “192.168.2.102”,“speech.mov”, 44100, 2, 16, 0.5, 2.0, .2} 4.2 Grouping Constructs

Media streams are grouped together when dependency between streams needs to be stated explicitly. In particular, grouping clusters one or more media streams or groups for synchronization. The groups are both dynamic and hierarchical.

Example 4: Suppose we have a video that shows a opera singer singing and we want to add the audio in lip synch mode. To keep up the impression that the soprano is really singing, if we speed up the video, we expect the audio to speed up as well. In order to provide this type of synchronization, we need to indicate that the audio and the video are somehow dependent on each other. Groups are an elegant and efficient way to specify synchronization on multiple streams. The following code groups the two streams.

group soprano = {“videostream_opera”,“audiostream_opera”}

Groups are hierarchical since a group member can be a previously declared group. They are dynamic since we have commands ungroup, to dissolve an existing group, add_group, to add elements to a group, delete_group to remove elements from a group, and regroup to add elements to a new group. Groups have sync points as well. They can either be given explicitly, or computed implicitly as the smallest value of the elements of the group (chosen so as not to lose precision).

4.3 Event Definition

Our constructs make heavy use of events. An event may be generated based on the characteristics of the multimedia streams. For example, the appearance of a particular face in a video stream or a particular voice in an audio stream might cause an event to be generated. The events in turn can affect the synchronization of multiple streams. Events are defined based on the satisfaction of one or more partial conditions. Partial conditions can involve the presence or absence of some signal, the matching of an attribute value or some other condition. Events have a destination (module or object or synchronization process) that they are sent to, as well start and end times and a priority.

Example 5: A user performs a right click of the mouse every time he or she wants to start a video clip; however the video clip cannot be started until the current video clip is terminated and the video must be terminated within a reasonably small range of time (within 5 seconds) otherwise the request is dropped.

partial_condition_signal_presence cond1 = { // Test for signal presence

NewVideoClip,

// Name of the signal – it is present when // the video is playing

yes }// Test for its presence

partial_condition_signal_presence cond2 = { RightClick,

// Present when user right clicks

yes,

// Test for presence (not absence)

0, 5 }

// It was present in last 5 seconds

event start_video = { player1,

// Destination of event is renderer

cond1,

// The partial conditions of the event

cond2 }

4.4 Synchronization

One basic synchronization construct is the loop. It has a number of elements which are played one or more times in sequence. The number of times the loop is repeated can be specified along with a delay time. Example 6: In the following example, the second video stream is played three seconds after the first. The pair repeats two times.

loop {

times = 2,

element = video_stream1,

delay = 3,

element = video_stream2

};

Another important type of synchronization is when we want to play two or more streams concurrently. We support this type of synchronization with the parloop construct. The syntax is similar to the loop construct however the elements of the parloop are played in parallel rather than sequentially. Loops can also be nested as shown in the following example.

parloop {

times = 4,

element = audio_stream,

loop {

times = 2,

element = video_stream1,

element = video_stream2

}

}

We can also specify that we want two or more media streams to play in parallel (in other words start at the same time) and end at the same time as well in a parloop construct. In order for this to occur in general one or more of the streams must be stretched (scaled). In order

for the scaling to occur, the scaling constraints given as part of the Quality of Service requirements in the declaration of the stream must not be violated.

Loops and parloops are the basic constructs used for synchronization of periodic data streams. They are also the mechanism used to start the playback (rendering) of a multimedia data stream. If we wish to play a stream just once, we use a loop construct with a single element and a single loop time. Note also that the presence of a loop embedded in a program does not cause the execution of the rest of the program to wait until the playback finishes – the execution continues concurrently with the rendering of the media.

4.5 Preemption Constructs

Loops, including infinite loops can be ended prematurely in response to an event. For example, consider a situation where a sequence of advertisements are being displayed on a public terminal, and suddenly a weather warning must interrupt or terminate the current show to provide urgent news. The warning is sent as an asynchronous signal, which may generate an alert event and require showing a text stream, which explains the type of emergency. Other multimedia streams such as an audio signal or a video could follow the text. This situation requires the specification of an abortion of a loop based on the presence of an asynchronous signal (for example the pressing of a button). The advertisement is put inside a loop, and the text media is displayed after the asynchronous signal aborts the loop. There are 2 types of abortion: "strong", "weak" which can be specified in the loop or parloop construct:

Strong abortion performs the immediate interruption at the next multimedia sync point without waiting for the completion of the current cycle of the loop as soon as an aperiodic signal is present.

Weak abortion performs preemption as soon an aperiodic signal is present but will complete the “current”loop cycle that is playing when the signal occurs.

Suppose that we have declared a group consisting of a video stream – MyAdvertisement, a text stream – MyText, and an audio stream – MyAudio. Further assume that we have declared sync points every two seconds for this group. If we want to stop playing MyAdvertisement when an aperiodic signal named StopAdv is present, we can do this as follows:f

loop {

times = 3,

abort_when = StopAdv,

abort_type = strong,

element = MyAdvertisement

}

In this example, even though the abort type is strong, we will wait until the next sync point in the media stream to abort the rendering of the stream in order to maintain synchronization with other members of the group. In the worst case, we will wait 2 seconds from the time the signal is present until the abortion occurs.

Suppose the advertisement is shown in sequence with some text. Suppose further that in the presence of the aperiodic signal StopAdv we want to skip the rest of the sequence of ads and text, and skip to the song which is supposed to follow them. However, we don’t want to interrupt an advertisement which has already started. In this case we can use weak abortion as shown below.

loop {

times = 1,

loop {

times = 1,

abort_when = StopAdv,

abort_type = weak,

element = MyAdvertisement,

loop {

times = 3,

element = MyText

}

}

element = Song

}

We can further control the weakness of the abortion and specify other possible synchronization situations by introducing the delayed abort. In this case, the delay value is added to the time required to reach the first synch point after the delay is over. That means that the media stream is rendered for the delay period plus the time to reach the first sync point after the delay is over. Again, let us consider an example.

loop {

times = 1,

abort_when = StopAdv,

delay = 3,

element = MyAdvertisement

}

In this example, since MyAdvertisement has sync points every 2 seconds and assuming that strong abortion is the default, the abort will occur between 3 and 5 seconds after presence of the signal StopAdv. If the loop ends before this time, no further delay occurs.

5 Related Research

Athwal [12f] presents a methodology for the synchronization of multimedia streams for engineering and scientific analysis. Since the scientific and engineering phenomena which are recorded and subsequently played back are frequently not well correlated to the human’s visual and cognitive timeframe, it is quite possible that the previously captured data must be played back in a different timeframe – perhaps using slow motion or time lapse or some more complex variability in the playback rate. This is termed time elasticity and it has some relationship to our notion of stretching grouped multimedia streams. It should be noted that the methods described in [12] are suitable only for prerecorded multimedia streams and that much of the methodology is concerned with minimizing resource usage during the synchronized play back of such streams.

Besides the limitations as far as application area and type of multimedia streams, the focus of that work is different from our research in that the focus is on implementation details for systems for synchronization rather than on languages to allow for the expression of synchronization. The work also differs in that it lacks the notion of sync points, which can be defined for our groups and loops, which allow a high level of flexibility for synchronizing multimedia streams under many different quality of service requirements. Furthermore, interaction of multimedia streams with aperiodic signals is not even considered. The same points about the difference of focus of our work and this one could be made about most of the other recent research on synchronization.

Cameron [13] proposes a model for reactivity in multimedia systems; however their notion of reactivity is much different than ours. They discuss multimedia systems in which a multimedia artifact (i.e. a multimedia stream) can react to discrete events, such as an audio player reaching the end of a track as well as to continuously evolving behaviors such as the volume of an audio track. They make a distinction between a series of discrete events and a continuously evolving behavior. Since behavior is an author-level abstraction, which therefore hides implementation details of the media streams, the approach is more suited for use as a high-level authoring tool for multimedia presentations rather than for construction of distributed multimedia systems.

A number of XML-based multimedia languages have been proposed lately. None of them provide all of the capabilities described in this paper, although some provide complementary capabilities. For example, Gu [14] introduces HQML, an XML-based language to express the quality of service requirements of distributed multimedia systems. Another example is the multi-modal presentation markup language (MPML) [15] which is an easy to use XML-based language enabling authors to script web-based interaction scenarios featuring life-like animated characters.

6 Conclusions and Future Research

A model for distributed multimedia systems which incorporates the synchronization constructs discussed in this paper along with an active repository which allows for the constant testing of the multimedia data for deterministic and non-deterministic events is given in [16]. The behavioral semantics of the language constructs have been developed as well in order to provide a formalism for verification, compilation, and validation. The semantics incorporates the temporality and the communication aspects of the system and uses a variation of the π-calculus [17] for modeling distributed reactive multimedia systems. The π-calculus has its roots in the CCS (Calculus of Communicating Systems) [18, 19, 20], which is able to describe interactive concurrent systems as well as traditional computation. The π-calculus adds to the CCS, mobility of the participating processes and uses the transmission of processes as values, and the representation of data structures as processes. This research will be presented in a future paper. References

1.Synchronized Multimedia Integration Language

2.0 Specification, http://www.w

https://www.sodocs.net/doc/e3104393.html,/TR/smil20/ Aug. 2001.

2. Virtual Reality Modeling Language, ISO/IEC14772, 1997 https://www.sodocs.net/doc/e3104393.html,/x3d/specifications/vrml/ISO_IEC_14772 -All/part1/concepts.html.

3. H. Kalva, L. Cheok, A. Eleftheriadis, “MPEG-4 Systems and Applications”, Proc. of the 7th ACM Intl. Conf. on Multimedia (Part 2), Orlando, Florida, pp. 192-192, October 1999.

4. R. Gordon, S. Talley, “Essential JMF – Java Media Framework”, Prentice Hall, 1999.

5. Object Management Group, “Control and management of A/V streams specification”, OMG Doc. telecom/97-05-07, 1997.

6. G. Berry, G. Gonthier, “The ESTEREL Synchronous Programming Language: Design, Semantics, Implementation,”Sci. of Comp. Progr. vol. 19, no. 2, pp. 87-152, Nov. 1992.

7. G. Berry, “The Foundations of Esterel”, in Proof, Language and Interaction: Essays in Honour of Robin Milner, G. Plotkin,

C. Stirling and M. Tofte ed., MIT Press, pp. 425-454, June 2000.

8. N.D. Georganas, R. Steinmetz, T. Nakagawa, “Guest Editorial on Synchronization Issues in Multimedia Communication”, IEEE J. on Sel. Areas in Comm. vol. 14, no. 1, pp. 1-4, 1996.

9. L. Li, A. Karmouch, N.D. Georganas, “Multimedia Teleorchestra with Independent Sources: Part 1&2 – Temporal Modeling of Collaborative Multimedia Scenarios”, ACM/Springer Multimedia Sys. vol. 1, no. 4, pp. 143-153, 1994.

10. L. Lamport, "Time, Clocks and the Ordering of Events in a Distributed System", Comm. of the ACM, vol. 21, no. 7,pp. 558-564, 1978.

11. R. Gordon, S. Talley, “Essential JMF – Java Media Framework”, Prentice Hall, 1999.

12. C.S. Athwal, J. Robinson, “Synchronized Multimedia for Engineering and Scientific Analysis”, Multimedia Systems, vol. 9, pp. 365-377, 2003.

13. H. Cameron, P. King, S. Thompson, “Modeling Reactive Multimedia: Events and Behaviors”, Multimedia Tools and Applications, vol. 19, pp. 53-77, 2003.

14. X. Gu, K. Nahrstedt, W. Yuan, D. Wichadakul, "An XML-based Quality of Service Enabling Language for the Web", J. of Visual Lang. and Comp. vol.13, no. 1, pp. 61-95, 2002.

15. H. Prendinger, S. Descamps, M. Ishizuka, “MPML: a Markup Language for Controlling the Behavior of Life-like Characters”, J. of Visual Lang. and Comp. vol. 15, pp. 183-203, 2004.

16. A. Guercio, A.K. Bansal, “TANDEM - Transmitting Asynchronous Non Deterministic and Deterministic Events in Multimedia Systems over the Internet”, Proc, of DMS 2004, pp. 57-62.

17. R. Milner, “Communicating and Mobile Systems; the π-calculus”, Cambridge University Press, 1999.

18. R. Milner, “A Calculus of Communicating Systems”, LNCS, vol. 92, Springer-Verlag, 1980.

19. R. Milner, “Communication and Concurrency”, Prentice Hall, 1989.

20. Y. Wang, “CSS + Time = an Interleaving Model for Real Time”, LNCS 510, pp. 217-228, 1991.

1 Introduction On

On choice-o?ering imperatives Maria Aloni? 1Introduction The law of propositional logic that states the deducibility of either A or B from A is not valid for imperatives(Ross’s paradox,cf.[9]).The command (or request,advice,etc.)in(1a)does not imply(1a)(unless it is taken in its alternative-presenting sense),otherwise when told the former,I would be justi?ed in burning the letter rather then posting it. (1) a.Post this letter!? b.Post this letter or burn it! Intuitively the most natural interpretation of the second imperative is as one presenting a choice between two actions.Following[2](and[6])I call these choice-o?ering imperatives.Another example of a choice-o?ering imperative is (2)with an occurence of Free Choice‘any’which,interestingly,is licensed in this context. (2)Take any card! Like(1a),this imperative should be interpreted as carrying with it a permission that explicates the fact that a choice is being o?ered. Possibility statements behave similarly(see[8]).Sentence(3b)has a read-ing under which it cannot be deduced from(3a),and‘any’is licensed in(4). (3) a.You may post this letter.? b.You may post this letter or burn it. (4)You may take any card. In[1]I presented an analysis of modal expressions which explains the phe-nomena in(3)and(4).That analysis maintains a standard treatment of‘or’as logical disjunction(contra[11])and a Kadmon&Landman style analysis of‘any’as existential quanti?er(contra[3]and[4])assuming,however,an in-dependently motivated‘Hamblin analysis’for∨and?as introducing sets of alternative propositions.Modal expressions are treated as operators over sets of propositional alternatives.In this way,since their interpretation can depend on the alternatives introduced by‘or’(∨)or‘any’(?)in their scope,we can account for the free choice e?ect which arises in sentences like(3b)or(4).In this article I would like to extend this analysis to imperatives.The resulting theory will allow a uni?ed account of the phenomena in(1)-(4).We will start by presenting our‘alternative’analysis for inde?nites and disjunction. ?ILLC-Department of Philosophy,University of Amsterdam,NL,e-mail:M.D.Aloni@uva.nl

1.introduction

Introdution

Mike Jian

INTRODUCTION ?Section A: ?Comprises 8 two mark and 4 one mark multiple choice questions. ?Section B: ?Four 10 mark questions. ?Two 20 mark questions.

INTRODUCTION The examination is a three hour paper with 15 minutes reading and planning time. All questions are compulsory. Some questions will adopt a scenario/case study approach. All those questions will require some form of written response although questions on planning or review may require the calculation and interpretation of some basic ratios.

1.Which TWO of the following should be included in an audit engagement letter? ①Objective and scope of the audit ②Results of previous audits ③Management’s responsibilities ④Need to maintain professional scepticism A.① and ② B.① and ③ C.② and ④ D.③ and ④ (2 marks)

外文翻译关于Linux的介绍(Introduction to Linux)

毕业设计说明书 英文文献及中文翻译 学 专 指导教师： 2014 年 6 月

Introduction to Linux 1.1 History 1.1.1 UNIX In order to understand the popularity of Linux, we need to travel back in time, ab out 30 years ago... Imagine computers as big as houses, even stadiums. While the sizes of those com puters posed substantial problems, there was one thing that made this even worse: eve ry computer had a different operating system. Software was always customized to ser ve a specific purpose, and software for one given system didn't run on another system. Being able to work with one system didn't automatically mean that you could work w ith another. It was difficult, both for the users and the system administrators. Computers were extremely expensive then, and sacrifices had to be made even after th e original purchase just to get the users to understand how they worked. The total cost of IT was enormous. Technologically the world was not quite that advanced, so they had to live with t he size for another decade. In 1969, a team of developers in the Bell Labs laboratories started working on a solution for the software problem, to address these compatibility issues. They developed a new operating system, which was simple and elegant written in the C programming language instead of in assembly code able to recycle code. The Bell Labs developers named their project "UNIX." The code recycling features were very important. Until then, all commercially av ailable computer systems were written in a code specifically developed for one system . UNIX on the other hand needed only a small piece of that special code, which is now commonly named the kernel. This kernel is the only piece of code that needs to be ad apted for every specific system and forms the base of the UNIX system. The operating system and all other functions were built around this kernel and written in a higher pr ogramming language, C. This language was especially developed for creating the UNI

自我介绍(self-introduction)

自我介绍(self-introduction) ??? 1. Good morning. I am glad to be here for this interview. First let me introduce myself. My name is ***, 24. I come from ******,the capital of *******Province. I graduated from the ******* department of *****University in July ,2001.In the past two years I have been preparing for the postgraduate examination while I have been teaching *****in NO.****middle School and I was a head-teacher of a class in junior grade two. Now all my hard work has got a result since I have a chance to be interview by you . I am open-minded ,quick in thought and very fond of history.In my spare time,I have broad interests like many other youngsters.I like reading books, especially those about *******.Frequently I exchange with other people by making comments in the forum on line.

加拿大介绍Canada Introduction

Canada Introduction Canada has a population just less than 30 million people in a country twice the area of the United States. The heritage of Canada was French and English; however, significant immigration from Asia and Europe's non-French and English countries has broadened Canada's cultural richness. This cultural diversity is considered a national asset, and the Constitution Act prohibits discrimination against individual citizens on the basis of race, color, religion, or sex. The great majority of Canadians are Christian. Although the predominant language in Canada is English, there are at least three varieties of French that are recognized: Quebecois in Quebec, Franco-Manitoban throughout Manitoba and particularly in the St. Boniface area of Winnipeg, and Acadian. The Italian language is a strong third due to a great influx of Italian immigrants following W.W.II. Canada's three major cities are distinctively, even fiercely different from one another even though each is a commercially thriving metropolitan center. Montreal, established in the 17th century and the largest French city outside France, has a strong influence of French architecture and culture. It is a financial and manufacturing center

英语口语集锦-介绍(introduction)

英语口语集锦－介绍(introduction) making introductions 给人作介绍 1. jane, tom. tom, jane. 2. jane, this is tom, tom, this is jane. 3. jane, i’d like you to meet my friend tom. 4. jane, have you met tom? 5. jane, do you know tom? 6. look, tom’s he re. tome, come and meet jane. 7. jane, this is tom. he’s a friend from college. 8. jane, tom is the guy i was telling you about. 9. do you know each other? 10. have you two met ? 11. have you two been introduced? 12. allow me to introduce professor linda ferguson of harvard university. 13. let me introduce our guest of honor, mr.david morris. 14. if you want to be introduced to the author, i think i can arrange it.

making a self-introduction 作自我介绍 1. may i introduce myself 2. hello, i’m hanson smith. 3. excuse me, i don’t think we’ve met. my name’s hanson smith. 4. how do you do? i’m hanson smith. 5. i’m david anderson. i don’t believe i’ve had the pleasure. 6. first let me introduce myself. i’m peter white, production manager. 7. my name is david. i work in the marketing department. after being introduced. 被介绍与对方认识后. 1. i’m glad to meet you. 很高兴认识你. 2. nice meeting you. 很高兴认识你. (平时用得最多的是nice to meet you ) 3. how nice to meet you. 认识你真高兴. 4. i’ve heard so much about you. 我知道很多关于你的事儿. 5. helen has told me all about you. 海伦对我将了好多你的事儿. 6. i’ve been wanting to meet you for some time.

英语自我介绍(self-introduction)模板

英语自我介绍例文模板： Sample1 My name is ________. I am graduate from ________ senior high school and major in ________. There are ________ people in my family. My father works in a computer company. And my mother is a housewife. I am the youngest one in my family. In my spare time, I like to read novels. I think reading could enlarge my knowledge. As for novels, I could imagine whatever I like such as a well-known scientist or a kung-fu master. In addition to reading, I also like to play PC games. A lot of grownups think playing PC games hinders the students from learning. But I think PC games could motivate me to learn something such as English or Japanese. My favorite course is English because I think it is interesting to say one thing via different sounds. I wish my English could be improved in the next four years and be able to speak fluent English in the future. Sample2: I am . I was born in . I graduate from senior high school and major in English. I started learning English since I was 12 years old. My parents ha ve a lot of American friends. That’s why I have no problem communicating with Americans or others by speaking English. In my spare time, I like to do anything relating to English such as listening to English songs, watching English movies or TV programs, or even attending the activities held by some English clubs or institutes. I used to go abroad for a short- term English study. During that time, I learned a lot of daily life English and saw a lot of different things. I think language is very interesting. I could express one substance by using different sounds. So I wish I could study and read more English literatures and enlarge my knowledge. Sample3: My name is . There are 4 people in my family. My father is a Chemistry teacher. He teaches chemistry in senior high school. My mother is an English teacher. She teaches English in the university. I have a younger brother, he is a junior high school student and is preparing for the entrance exam. I like to read English story books in my free time. Sometimes I surf the Internet and download the E- books to read. Reading E- books is fun. In addition, it also enlarges my vocabulary words because of the advanced technology and the vivid animations. I hope to study both English and computer technology because I am interested in both of the subjects. Maybe one day I could combine both of them and apply to my research in the future. Sample4: My name is . I am from . There are people in my family. My father works in a computer company. He is a computer engineer. My mother works in a international trade company. She is also a busy woman. I have a older sister and a younger brother. My sister is a junior in National Taiwan University. She majors in

用英语Introduction 介绍

Introduction 介绍 Making introductions 给人作介绍 1. Jane, Tom. Tom, Jane. 2. Jane, this is Tom, Tom, this is Jane. 3. Jane, I'd like you to meet my friend Tom. 4. Jane, have you met Tom? 5. Jane, do you know Tom? 6. Look, Tom's here. Tome, come and meet Jane. 7. Jane, this is Tom. He's a friend from college. 8. Jane, Tom is the guy I was telling you about. 9. Do you know each other? 10. Have you two met ? 11. Have you two been introduced? 12. Allow me to introduce Professor Linda Ferguson of Harvard University. 13. Let me introduce our guest of honor, Mr.David Morris. 14. If you want to be introduced to the author, I think I can arrange it. Making a self-introduction 作自我介绍 1. May I introduce myself 2. Hello, I'm Hanson Smith. 3. Excuse me, I don't think we've met. My name's Hanson Smith. 4. How do you do? I'm Hanson Smith. 5. I'm David Anderson. I don't believe I've had the pleasure. 6. First let me introduce myself. I'm Peter White, production manager. 7. My name is David. I work in the marketing department. After being introduced. 被介绍与对方认识后 1. I'm glad to meet you. 很高兴认识你。 2. Nice meeting you. 很高兴认识你。 3. How nice to meet you. 认识你真高兴。 4. I've heard so much about you. 我知道很多关于你的事儿。 5. Helen has told me all about you.

希腊罗马神话1. Introduction

1 Introduction Greco-Roman mythology is the cultural reception of myths from the ancient Greeks and Romans. Along with philosophy and political thought, mythology represents one of the major survivals of classical antiquity throughout later Western culture. Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece and are part of religion in modern Greece and around the world as Hellenismos. Modern scholars refer to, and study the myths in an attempt to throw light on the religious and political institutions of Ancient Greece, its civilization, and to gain understanding of the nature of myth-making itself. Roman mythology is the combination of the beliefs, the rituals, and the observances of supernatural occurrences by the ancient Romans from early periods until Christianity finally completely replaced the native religions of the Roman Empire. The religion of the early Romans was so changed by the addition of numerous and conflicting beliefs in later times, and by the assimilation of a vast amount of Greek mythology, that it cannot be ever reconstructed precisely. This was because of the extensive changes in the religion before the literary tradition began. Most of the Greek deities were adopted by the Romans, although in many cases there was a change of name. Much of what became Roman mythology was borrowed from Greek mythology at a later date, as Greek gods were associated with their Roman counterparts. Greek mythology is embodied, explicitly, in a large collection of narratives, and implicitly in Greek representational arts, such as vase-paintings and votive gifts. Greek myth attempts to explain the origins of the world, and details the lives and adventures of a wide variety of gods, goddesses, heroes, heroines, and mythological creatures. These accounts initially were disseminated in an oral-poetic tradition; today the Greek myths are known primarily from Greek literature. The oldest known Greek literary sources, the epic poems Iliad and Odyssey, focus on events surrounding the Trojan War. Two poems by Homer's near contemporary Hesiod, the Theogony and the Works and Days, contain accounts of the genesis of the world, the

Introduction 介绍

Introduction 介绍 一、Introducing Each other 介绍相识 高频语句 自我介绍 1.May I introduce myself to you? 我可以作自我介绍吗？ 2.Did you meet before? 我们见过面吗？ 3.Allow me to introduce myself. 请允许我作个自我介绍。 4.Hello, my name is Bill. 你好，我叫比尔。 5.Can you just introduce yourself to the other guests? 您向其他客人自我介绍一下， 好吗？ 6.Are you Mr. Smith? 你是史密斯先生吗？ 7.Do you mind if I join you? 我加入你们当中来，介意吗？ 8.Here is my card. 这是我的命。 9.It’s really an honor for me to meet you. 真的很荣幸认识你。 10.This is the first time we have met. 这是我们第一次见面。 介绍同事 1.I’d like you to meet Mary, my colleague. 我介绍你们认识玛丽，我的同事。 2.Will you introduce me to that lady? 把我介绍给那位女士认识一下，好吗？ 3.I don’t think you have known each other. 我想你们俩还互不认识吧。 4.Just go in and meet everyone. 进去和大家认识一下。 5.May I introduce Mr. Chen？让介绍一下陈先生好吗？ 相互寒暄 1.We have been looking forward to meeting you. 我们一直盼望着见到您。 2.I’m delighted to know you. 很高兴认识你。 3.Is this your first visit to Shanghai? 这是您第一次来上海？ 4.I can show you around while you’re here. 您在此逗留期间我可以带着您到处 走走。 5.Mr. Li has told me all about you. 李先生对我讲了好多你的事儿。 二、Products Introduction 产品介绍