Method and apparatus for prefetching content in a data stream

Abstract

A data-processing system facilitates processing a data stream to assist other devices to pre-fetch elements of the data stream, out-of-sequence, for uninterrupted playback. During operation, the system can receive a data file, and segments the data file into a sequence of content objects. The system then determines a target content object that is to be processed out-of-sequence, and a corresponding source content object. The system then inserts a reference to the target content object, into the source content object, and stores the sequence of content objects. A client device can disseminate interest to obtain the data stream's content objects. Upon receiving a content object, the client device can determine whether the content object includes a reference to other content objects. If so, the client device can disseminate interests for these referenced content objects.

Description

RELATED APPLICATION

The subject matter of this application is related to the subject matter of the following application:

• • U.S. patent application Ser. No. 13/720,736, entitled “DYNAMIC ROUTING PROTOCOLS USING DATABASE SYNCHRONIZATION,” by inventors Van L. Jacobson and Marc E. Mosko, filed 19 Dec. 2012;the disclosures of which are incorporated by reference in their entirety herein.

BACKGROUND

Field

This disclosure is generally related to a system for transferring a data stream to a client device. More specifically, this disclosure is related to a method for segmenting a data stream into a sequence of content objects, and using a reference in a content object to obtain one or more other out-of-sequence content objects from the data stream.

Related Art

Widespread use of the Internet has made it easier for people to consume digital content without traveling to a store to purchase physical copies. A user's client device can obtain the digital content, such as streaming media and executable files, from a dedicated server. For example, media playing programs can present a media stream to the user while the media stream is being downloaded, when the media stream is encoded into a predetermined sequence of frames that are to be processed in-order.

Some media formats require a media player to seek or skip to other portions of the media stream to read the necessary portions before resuming playback. However, web browsers and download managers typically download data files in-sequence. Hence, presenting the media stream during download can require the media player to pause playback of the content until the necessary portions are downloaded, which leads to an interrupted playback experience. Similarly, when operating systems download a binary executable file to execute for the user, the entire file needs to be downloaded before the file can be executed. However, downloading complete software applications can cause the user to wait for an undesirably long period of time, especially when the executable files are significantly large.

SUMMARY

One embodiment provides a data-processing system that facilitates processing a data stream out-of-sequence for uninterrupted playback. During operation, the system can receive a data file, and segments the data file into a sequence of content objects. The system then determines a target content object that is to be processed out-of-sequence and a source content object for the target content object. Source content objects are content objects that are to be processed preceding the target content objects. The system then inserts a reference indicating the target content object into the source content object, and stores the sequence of content objects.

In some embodiments, the data file includes a plurality of data items, wherein a content object's boundaries can coincide with a data item's beginning boundary, ending boundary, or an offset between the beginning and ending boundaries.

In some embodiments, the reference comprises one or more of an identifier for a target object, and a data offset within the target content object. The target object identifier indicates which content object will be processed next, and the data offset indicates an offset within the target content object.

In some embodiments, the content object contains a name containing a hierarchically structured variable-length identifier (HSVLI).

In some embodiments, the data file includes a media stream.

In some variations to these embodiments, the system encodes the media stream into a target format, and generates a data file that includes the media stream in the target format.

In some embodiments, the file type can include a media stream, a text stream, a command sequence, an executable file, a compressed file, an image file, an encrypted file, and/or any data format now known or later developed.

In some embodiments, the system determines that the content object is stored in a local repository, and sends the content object to an interface associated with the interest.

In some embodiments, the system publishes a sequence of content objects by disseminating an advertisement for the content object over a content-centric network.

One embodiment provides a client computer that can disseminate an interest for digital content. Upon receiving a content object corresponding to the digital content, the client computer determines that the received content object includes a reference to a data item from a target content object. The client computer then disseminates an interest for the target content object to obtain the data item.

In some embodiments, the system generates an interest for a successive content object in the sequence, and disseminates the interest to obtain the successive content object. In doing so, the system processes data in-sequence when there are no references to target content objects.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an exemplary computer system that facilitates processing data files from various local and remote computing devices in accordance with an embodiment.

FIG. 2A illustrates a media stream which has been segmented into a plurality of content objects in accordance with an embodiment.

FIG. 2B illustrates information provided by a content object in accordance with an embodiment.

FIG. 2C illustrates information provided by reference data in accordance with an embodiment.

FIG. 3 presents a flow chart illustrating a method for segmenting a data file and inserting a reference into a content object in accordance with an embodiment.

FIG. 4 presents a flow chart illustrating a method for determining a target object for which to generate a reference in accordance with an embodiment.

FIG. 5 presents a flow chart illustrating a method for encoding a media stream to a target format in accordance with an embodiment.

FIG. 6 presents a flow chart illustrating a method for generating interests and obtaining content objects in accordance with an embodiment.

FIG. 7 illustrates an exemplary apparatus that facilitates receiving and processing a data stream over a content-centric network in accordance with an embodiment.

FIG. 8 illustrates an exemplary computer system that facilitates receiving and processing a data stream over a content-centric network in accordance with an embodiment.

In the figures, like reference numerals refer to the same figure elements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Overview

Embodiments of the present invention provide a content-streaming system that solves the problem of interrupted streaming of content to a user when the streaming content includes data that is to be processed out-of-sequence. During operation, the system inserts references while segmenting the data into content objects. For example, a server can segment a media stream or file into a sequence of content objects, and can serve these content objects to satisfy interests for the file or for a specific content object. While segmenting the data file, the system can determine which target content objects are to be processed out-of-sequence, and determines source content objects that are to be processed preceding these target content objects. The system then inserts references into these source content objects to indicate the target content object, and an offset within these target content object.

In the disclosure, the term “successive” content object refers to a content object that is to be processed following a source content object in a data stream's predetermined sequence of content objects.

In some embodiments, the data file can include a plurality of data items, and the content object boundaries may not always be aligned with a data item's beginning or ending boundaries. For example, the system may generate the content objects to have a predetermined fixed length, or may generate the content objects to have a variable length for including one or more data items. In any case, the system generates the reference to indicate a content object, and to indicate an offset form which the target data item begins within the content object. A client device can decode a reference from a content object to obtain a recommendation for other content objects to cache or process next.

Streaming Data Out-of-Sequence

Typical data streaming techniques often produce adequate streaming results when the stream's data is to be processed in-sequence, but fail to produce an acceptable user experience if the stream's data items are to be processed out-of-sequence. Specifically, a client device may disseminate an interest for a data stream hosted by a remote content server, and the content server may stream the data stream in-sequence. However, if the client device needs to perform out-of-sequence processing of the stream's data items, the client device may need to interrupt the processing of the data stream until the client device receives a desired data item. For example, the client device may need to process a non-streaming video file whose index is located at the end of the file. In such a case, a typical client device would need to download the complete file in order to use the index to determine a media format for each audio or video data item, and/or to determine which data item to play next.

FIG. 1 illustrates an exemplary computer system 100 that facilitates processing data files from various local and remote computing devices in accordance with an embodiment. Computer system 100 can include a client device 104, which can include a computer, a tablet, a smartphone, or any other device with computational capability and a network-interfacing mechanism for communicating data over network 102. A client device 104 can obtain data by generating and disseminating an interest for the data. The interest may be satisfied locally by an application within the client device, or by a remote device accessible via a network 102.

For example, client device 104 can include or be coupled to a storage device 124, which may store content objects 126, content-requesting software 128, a media player 130, and an operating system 132. Media player 130 and/or operating system 132 can use content-requesting software 128 to disseminate an interest for data (e.g., a media stream). If the data's content objects are stored locally, client device can satisfy the interest using content objects 126. Otherwise, client device 104 disseminates the interest over network 102, which allows a remote network device 110 or a content server 108 to satisfy the interest.

Content server 108 can include or be coupled to a storage device 112, which may store data items 114, and a media streams 116. Further, content server 108 can process data items 114 and media streams 116 to generate content objects 118, and can store content objects 118 in storage device 112. Data items 114 can include any type of data including a media stream, a text document, an encrypted message, and executable files.

Network 102 can generally include any type of wired or wireless communication channel capable of coupling together various computing nodes. This includes, but is not limited to, a local area network, a wide area network, a wireless cellular network, or a combination of networks. In one embodiment of the present invention, network 102 implements a content-centric network.

FIG. 2A illustrates a data stream 200 which has been segmented into a plurality of content objects 212 in accordance with an embodiment. Data stream 200 can comprise a plurality of data items 202 that includes video data items, audio data items, and metadata for data stream 200. In some embodiments, some content objects can include a reference that indicates a recommendation for data from one or more other content objects. For example, content objects 212.1-212.14 may include a reference to metadata 202.5, which indicates how a media player is to process the video and audio data items 202.1-202.4. Hence, the first content object for each video or audio item 202.1-202.4 may include a reference to the start of metadata 202.5 at content object 212.14. Metadata 202.5 can include each of video and audio segments 202.1-202.4, a media-data description that includes formatting information and a playback configuration for the corresponding media data. Each of these media-data descriptions in metadata 202.5 may also include a reference to the corresponding video or audio segment that it describes (e.g., reference 214.5 for video data 202.3, starting at an offset 216 of content object 212.7). While processing the content objects for each audio or video data item (e.g., while processing content object 212.1), the client device can generate interest for both the referenced metadata 202.5 (content object 212.14) as well as for a successive content object (e.g., content object 212.2 following content object 212.1).

In some embodiments, a content object may not include reference data, such as content objects 212.2 and 212.3. While processing these content objects, the client device can generate an interest for the successive content object in the sequence. For example, when the client device determines that content object 212.3 does not include a reference, the client device generates an interest for the successive content object 212.4 to be processed following content object 212.3.

Data stream 200 can also include information other than media streams. For example, data stream 200 can include blocks of executable code that form an application that can be executed before the complete application is downloaded. Each data item 202 can correspond to one or more basic blocks of code, and each reference 214 can correspond to a jump or branch operation to a target block of code and/or for other application resources. Specifically, the client device may execute the code before receiving the full application. As in a media stream, the client device may receive the code in the form of content objects. While executing code from one content object, the client device can disseminate interest for other content objects that are referenced by the current content object, which allows the client device to download urgent application resources before non-urgent application resources.

Data stream 200 may also be simple file formats, such as compressed image files (e.g., a graphical interchange format (GIF) file) or other compressed data. Data stream 200 can include a sequence of protocol blocks and sub-blocks representing graphics elements of the GIF file. Each data item 202 can correspond to one or more blocks of data containing protocol blocks or sub-blocks, and each reference 214 can correspond to a shift to an unrelated graphic element. Using the references, the client device may decode and display a GIF image without any unnecessary shifts to unrelated graphics elements. In doing so, the client device can minimize the number of hardware parameter resets and the delays that correspond to parameter resets when loading a GIF image.

FIG. 2B illustrates information provided by a content object 250 in accordance with an embodiment. Content object 250 can include a location-independent structured name 252, such as a hierarchically structured variable-length identifier (HSVLI). Additionally, content object 250 can include metadata 254, payload 256, and a signature 258. Metadata 254 can include general information necessary for clients and servers to send or receive the appropriate content objects. Payload 256 can include the data items located in a content object. Content object 250 may also include a reference 260, which references data from a target content object. In some embodiments, only some content objects in a data stream include reference 260 for data that is to be processed out-of-sequence.

FIG. 2C illustrates information provided by reference data 270 in accordance with an embodiment. Specifically, reference data 270 includes a content object identifier 272 and a data offset 274, which together recommend a data item to process or cache for the user. Content object identifier 272 indicates another content object that needs to be processed or cached next, and data offset 274 indicates the start of the recommended data item from the content object. In some variations, an instance of reference data 270 does not include an explicit data offset 274, which implies that the start of the referenced data item is aligned with the start of the content object.

FIG. 3 presents a flow chart illustrating a method for segmenting a data file and inserting a reference into a content object in accordance with an embodiment. During operation, the system segments a data file into a sequence of content objects (operation 302). These content objects function as data packets that facilitate transferring the data file to a remote device, and are stored in a CCN repository to satisfy interests for the data file or for a specific content object.

After segmenting the file into content objects, the system analyzes the content objects to determine one or more target content objects that are to be processed out-of-sequence by a client device (operation 304). The system then determines, for each target content object, the source object after which the target content object is to be processed (operation 306). The system inserts a reference into the source content object, which indicates a recommendation for a data item in the target content object (operation 308). A client device can use the embedded recommendation to process or cache the target content object following the source content object. In some embodiments, the reference includes information indicating a location-independent identifier for the target content object (e.g., an HSVLI name), and the data offset within the target content object. The system then determines whether there are more content objects to be processed out-of-sequence (operation 310). If target content objects remain, the system returns to operation 304. Otherwise, the system proceeds to publish the content objects that together make up the data file (operation 312). The system can publish a content object by disseminating an advertisement for the content object over a content-centric network.

FIG. 4 presents a flow chart illustrating a method for determining a target content object for which to generate a reference in accordance with an embodiment. The system begins by selecting a file-data offset of the data file, which is to be processed out-of-sequence (operation 402). For example, the data file may be an executable file or a media stream that includes data items that are to be processed out-of-sequence, and determines an offset, from the start of the data file, for each of these data items. The system then determines which content object corresponds to the file-data offset (operation 404), and determines a content-object offset, from the start of the content object, that corresponds to the target data item (operation 406). The target content object and the content object's offset together make up the reference to the data item mapped to by the file-data offset.

FIG. 5 presents a flow chart illustrating a method for encoding a media stream to a target format in accordance with an embodiment. During operation, the system selects a data file to publish (operation 502). Data files include, but are not limited to, a data item, a CCN content object, a media stream, an executable program, etc. In one embodiment, the system determines whether the data file includes a media stream (operation 504), and if so, encodes the contents of the media stream to a target format (operation 506). The system then generates a data file to include the media stream in the target format (operation 508). Subsequently, the system generates the sequence of content objects using the target-formatted data file (operation 512). Note that each content object may have a starting or ending boundary that is aligned with a data item's starting boundary, ending boundary, or an offset between the data item's starting and ending boundaries.

Otherwise, if the data file does not include a media stream, the data file is in the target format, and the server proceeds to generate the sequence of content objects for the data file (operation 510).

In some embodiments, the system can also encode other data streams into a different target format that facilitates processing data out-of-sequence, before downloading the complete file. For example, the data stream can include a presentation (e.g., a PowerPoint document), executable code, etc. Then, during operation 506, the system can encode the data stream into a target format that facilitates accessing individual data items of the data stream as needed, such as into a sequence of images, a sequence of instruction-code blocks, etc.

FIG. 6 presents a flow chart illustrating a method for generating interests and obtaining content objects in accordance with an embodiment. Recall that some content objects from a data stream may include references to a data item of a target content object. During operation, a client generates and disseminates an interest for a piece of content across a content-centric network (operation 602). After disseminating the interest, the client receives the content object corresponding to the interest (operation 604), and determines whether the received content object includes a reference to a data item from a target content object (operation 606).

If the content object is found to include a reference to a target content object, the client disseminates an interest corresponding to the reference to obtain the target content object (operation 608). In some embodiments disseminating the interest causes routers of a content-centric network to propagate the interest to a content server that stores the content object. However, if the content object does not include a reference, the system can proceed to operation 610.

The client device then determines whether more content objects exist for the data stream (operation 610). If the client determines that there are no more content objects to obtain for the data stream, the client device has received all the content objects that make up the data stream and ends the process. Otherwise, the client device generates an interest for a successive content object (operation 612), and disseminates the interest corresponding to the successive content object (operation 614).

In some embodiments, after disseminating an interest (e.g., at operation 608 or operation 614), the system returns to operation 604 to receive more content objects for the data stream.

FIG. 7 illustrates an exemplary apparatus 700 that facilitates receiving and processing a data stream over a content-centric network in accordance with an embodiment. Apparatus 700 can comprise a plurality of modules which may communicate with one another via a wired or wireless communication channel. Apparatus 700 may be realized using one or more integrated circuits, and may include fewer or more modules than those shown in FIG. 7. Further, apparatus 700 may be integrated in a computer system, or realized as a separate device which is capable of communicating with other computer systems and/or devices. Specifically, apparatus 700 can comprise an interest-disseminating module 702, a content object-receiving module 704, a reference-determining module 706, an interest-generating module 708.

During operation, once a client device generates an interest, interest-disseminating module 702 disseminates this interest over a content-centric network. After the interest is disseminated, if content objects are returned, content object-receiving module 704 receives these content objects. Reference-determining module 706 is then able to determine whether these content objects contain references to target content objects. If these content objects contain references, interest-disseminating module 702 disseminates an interest which corresponds to the reference. Otherwise, or additionally, interest-generating module 708 generates an interest which corresponds to a successive content object. Once again, interest-disseminating module 702 then disseminates an interest for the successive content object.

FIG. 8 illustrates an exemplary computer system 802 that facilitates receiving and processing a data stream over a content-centric network in accordance with the presence or lack of a reference. Computer system 802 includes a processor 804, a memory 806, and a storage device 808. Memory 806 can include a volatile memory (e.g., RAM) that serves as a managed memory, and can be used to store one or more memory pools. Furthermore, computer system 802 can be coupled to a display device 810, a keyboard 812, and a pointing device 814. Storage device 808 can store operating system 816, data processing system 818, and data 828.

Data processing system 818 can include instructions which, when executed by computer system 802, can cause computer system 802 to perform methods and/or processes described in this disclosure. Specifically, data processing system 818 may include instructions for disseminating an interest for content over a content-centric network (interest-disseminating module 820), and can include instructions for receiving a content object that satisfies the interest (content object-receiving module 822).

Data processing system 818 can also include instructions to determine whether a content object includes a reference that recommends data from a target content object (reference-determining module 824). Data processing system 818 can also include instructions for generating an interest for a recommended content object and/or for a successive content object (interest-generating module 826). Further, interest-disseminating module 820 can disseminate the interest that has been generated for the recommended content object or the successive content object.

Data 828 can include any data that is required as input or that is generated as output by the methods and/or processes described in this disclosure.

The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer-readable media now known or later developed.

The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium.

Furthermore, the methods and processes described above can be included in hardware modules. For example, the hardware modules can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules.

The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A computer-implemented method comprising: segmenting, by a computer, digital content into a sequence of content objects;determining a target content object of the sequence of content objects, wherein the target content object is to be processed out-of-sequence;determining a source content object of the sequence of content objects, wherein the target content object is to be processed after the source content object;inserting a reference into the source content object, wherein the reference indicates that the target content object is to be processed following the source content object, wherein the reference is distinct from a name for the source content object; andstoring the sequence of content objects, wherein the sequence includes the reference inserted into the source content object.

2. The method of claim 1, wherein the digital content includes a plurality of data items, and wherein a content object's starting boundary or ending boundary corresponds to one or more of: a starting boundary of a data item;an ending boundary of a data item; andan offset between a data item's starting boundary and ending boundary.

3. The method of claim 1, wherein the reference comprises one or more of: an identifier for the target content object; anda data offset within the target content object.

4. The method of claim 3, wherein the identifier includes a hierarchically structured variable-length identifier.

5. The method of claim 1, wherein the digital content includes one or more of: an audio stream;a video stream;executable instructions;a document;a graphical interchange format file;encrypted code; anda text stream.

6. The method of claim 1, further comprising: encoding the contents of a source media stream to a target media-stream format; andgenerating the digital content to include the source media stream in the target media-stream format.

7. The method of claim 1, wherein determining the target object involves: determining a file-data offset of the data file, which is to be processed out-of-sequence; anddetermining, from the sequence of content objects, the content object that corresponds to the file-data offset.

8. The method of claim 1, further comprising: receiving an interest for a content object; andin response to determining that the content object is stored in a local repository, sending the content object through an interface associated with the interest.

9. The method of claim 1, further comprising publishing the sequence of content objects, wherein publishing a respective content object involves: disseminating an advertisement for the content object over a content-centric network.

10. A computer-implemented method comprising: disseminating, by a client computing device, an interest for digital content, wherein a name for the interest is a hierarchically structured variable length identifier comprised of contiguous name components ordered from a most general level to a most specific level;receiving a content object, which corresponds to the digital content and satisfies the interest;determining that the received content object includes a reference to a data item from a target content object, wherein the reference is distinct from a name for the received content object; anddisseminating an interest for the target content object to obtain the data item.

11. The method of claim 10, wherein the method further comprises: generating an interest for a successive content object; anddisseminating an interest, which corresponds to the successive content object, to obtain the successive content object.

12. The method of claim 10, wherein the data item's starting boundary corresponds to one or more of: a starting boundary of the target content object; andan offset from the target content object's starting boundary.

13. The method of claim 10, wherein the reference indicates: an identifier for the target content object; anda data offset, from the target content object's starting boundary, for the data item.

14. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method, the method comprising: segmenting, by a computer, digital content into a sequence of content objects;determining a target content object of the sequence of content objects, wherein the target content object is to be processed out-of-sequence;determining a source content object of the sequence of content objects, wherein the target content object is to be processed after the source content object;inserting a reference into the source content object, wherein the reference indicates that the target content object is to be processed following the source content object, wherein the reference is distinct from a name for the source content object; andstoring the sequence of content objects, wherein the sequence includes the reference inserted into the source content object.

15. The storage medium of claim 14, wherein the digital content includes a plurality of data items, and wherein a content object's starting boundary or ending boundary corresponds to one or more of: a starting boundary of a data item;an ending boundary of a data item; andan offset between a data item's starting boundary and ending boundary.

16. The storage medium of claim 14, wherein the reference comprises one or more of: an identifier for the target content object; anda data offset within the target content object.

17. The storage medium of claim 16, wherein the identifier includes a hierarchically structured variable-length identifier.

18. The storage medium of claim 14, wherein the digital content includes one or more of: an audio stream;a video stream;executable instructions;a document;a graphical interchange format file;encrypted code; anda text stream.

19. The storage medium of claim 18, further comprising: encoding the contents of a source media stream to a target media-stream format; andgenerating the digital content to include the source media stream in the target media-stream format.

20. The storage medium of claim 14, wherein determining the target object involves: determining a file-data offset of the data file, which is to be processed out-of-sequence; anddetermining, from the sequence of content objects, the content object that corresponds to the file-data offset.

21. The storage medium of claim 14, further comprising: receiving an interest for a content object; andin response to determining that the content object is stored in a local repository, sending the content object through an interface associated with the interest.

22. The storage medium of claim 14, further comprising publishing the sequence of content objects, wherein publishing a respective content object involves disseminating an advertisement for the content object over a content-centric network.

23. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method, the method comprising: disseminating an interest for digital content, wherein a name for the interest is a hierarchically structured variable length identifier comprised of contiguous name components ordered from a most general level to a most specific level;receiving a content object, which corresponds to the digital content and satisfies the interest;determining that the received content object includes a reference to a data item from a target content object, wherein the reference is distinct from a name for the received content object; anddisseminating an interest for the target content object to obtain the data item.

24. The storage medium of claim 23, wherein the method further comprises: generating an interest for a successive content object; anddisseminating an interest, which corresponds to the successive content object, to obtain the successive content object.

25. The storage medium of claim 23, wherein the data item's starting boundary corresponds to one or more of: a starting boundary of the target content object; andan offset from the target content object's starting boundary.