Patent Application
20070180151
The present invention generally relates to computer databases and more specifically to synchronization of duplicate databases on a network.
In many situations, communications between computers linked by a communications network is constrained to use a pre-defined protocol that includes a pre-defined set of message formats (e.g., Aeronautical Radio Inc. (ARINC) 1999, Data link ground system standard and interface specification (DGSS/IS), ARINC Specification 620-4, Annapolis, Md; and United States Department of Defense (US DOD) 1999, Tactical digital information link (TADIL) J message standard, MIL-STD-6016A, April 30). Use of a pre-defined protocol is essential for interoperability among independently-developed systems. The protocols required for two systems to interoperate are typically defined in several layers (e.g. the seven layers defined by the OSI reference model ISO/IEC 1994). Achieving interoperability between systems requires adherence to protocol specifications at all layers. Application-layer protocols for providing application-layer interoperability have been defined for a variety of purposes-file transfer, electronic mail, database access, web browsing, etc. A number of application-layer protocols have been defined for monitoring and control functions in aerospace, defense, industrial automation, telecommunications, and other industries.
Typically in these networks, one or more of the computers comprise a local information object that holds information to be shared with other computers. The local information object may be a database. Applications running on a computer read and update their local information object. To maintain information object synchronization between computers on the network, update operations that alter the local object of one computer must be communicated to the other computers. Two problems arise in maintaining information object synchronization. First, applications issue update operations to their local information objects in a format largely based on the structure of the local object. Because these update operations are not in the format of messages compliant with a pre-defined protocol, they cannot be directly communicated to other computers by a communications network that is constrained to use a pre-defined protocol. Second, because reducing communication cost is important in environments, such as wireless networks, where bandwidth is at a premium and availability is intermittent, information object synchronization must be achieved in a manner that efficiently utilized network bandwidth.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for efficiently communicating information object updates in protocol constrained communications networks.
The Embodiments of the present invention provide methods and systems for model driven message processing and will be understood by reading and studying the following specification.
In one embodiment, an information object replication system is provided. The system comprises a log adapted to store records; a request logging function adapted to record a sequence of updates sent by one or more local applications to a local information object in the log; and an update propagation function in communication with the log, the update propagation function adapted to communicate one or more messages to one or more remote information objects, wherein the one or more messages represent updates to the local information object based on the sequence of updates, the update propagation function is further adapted to generate the one or more messages based on application-layer message formats and message semantics defined by a message model.
In another embodiment, a method for propagating information object updates is provided. The method comprises logging a sequence of update requests made to a local information object by one or more applications; correlating the sequence of update requests with one or more message formats based on message semantics defined by a message model; encoding the sequence of update requests as one or more messages based on application-layer message formats defined by the message model; and communicating the one or more messages to one or more remote computer systems.
In still another embodiment, a computer-readable medium having computer-executable instructions for performing a method for propagating information object updates is provided. The method comprises logging a sequence of update requests made to a local information object by one or more applications; correlating the sequence of update requests with one or more message formats based on message semantics defined by a message model; encoding the sequence of update requests as one or more messages based on application-layer message formats defined by the message model; and communicating the one or more messages to one or more remote computer systems.
In yet another embodiment, an information object replication system is provided. The system comprises means for logging a sequence of update requests made to a local information object by one or more applications; means for correlating the sequence of update requests with one or more message formats based on message semantics defined by a message model, the means for correlating responsive to the means for logging; means for encoding the sequence of update requests as one or more messages based on application-layer message formats defined by the message model, the means for encoding responsive to the means for correlation; and means for communicating the one or more messages to one or more remote computer systems, the means for communicating responsive to the means for encoding.
Embodiments of the present invention can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which:
In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize features relevant to the present invention. Reference characters denote like elements throughout figures and text.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.
With embodiments of the present invention, a computer sends protocol compliant messages across a communications network to convey information introduced by local applications as updates to the computer's local information object. Remote computer systems receiving the messages apply corresponding updates to their own information objects so that copies of the information distributed among various computers on the network remain synchronized. Information object updates and network messages are correlated with each other by message formats and semantics defined by a messaging model.
In one embodiment, replication function 106 further comprises an update propagation function 114 coupled to communicate with log 112. Update propagation function 114 translates logged update requests into one or more messages allowed by the protocol constraints of communications link 118. In one embodiment, to conserve communications link 118 bandwidth, update propagation function 114 first transforms the logged update requests into a compressed sequence of requests as described in the '778 Application herein incorporated by reference.
To communicate updates applied to local information object 108 to one or more remote computers 124, update propagation function 114 follows a publish-subscribe message pattern using message formats compliant with a particular application-layer protocol. With a publish-subscribe message pattern, computer 102 sends locally-available information to one or more remote computers 124 on a periodic or event-driven basis. Publish-subscribe is also known by those skilled in the art as information push.
In one embodiment of the present invention, update propagation function 114 maps logged update requests into protocol compliant messages based on a messaging model. The messaging model defines 1) valid application-layer message formats for protocol compliant messages, 2) the state space structure and update operations which apply to the local information object 108, 3) and message semantics which correlate the update operations with protocol compliant messages. For each valid message of a protocol, the application-layer message format defines the permitted fields of the message, and the permitted type of information (string, real number, etc.) for each field. In one embodiment, the application-layer message format is defined using one of several standard notations such as, but not limited to, ASN. 1 (ITU 2002) and XML Schema (W3C 2004). A message's semantics are defined in terms of the state change it causes in an information object of a specific structure. The change is expressed as a sequence of update requests, q1, . . . , qn, that are sent to an information object to effect the change. The sequence of requests used can depend on the current state of the object.
For example, in one embodiment, an application-layer message format is defined as name(v1, . . . , vn), where v1, . . . , vn are permitted fields for the message name. In one embodiment, the semantics for the message name(v1, . . . , vn) are captured as a set of rules for the form in Table 1. In one embodiment, each rule comprises a precondition, pre1 . . . prem, and a sequence of requests that will cause the desired state change if the precondition is satisfied. name(ν1, . . . , νn)
name(ν1, . . . , νn)
Through the message semantics defined by the messaging model, each message's meaning is defined as one or more sequences of update requests. Conversely, the messaging model also correlates sequences of update requests with one or more specific messages. In one embodiment, update propagation function 114 evaluates the contents of log 112, recognizes sequences of update requests defined by message semantics, and correlates the recognized sequences to one or more of the permitted message formats.
In one embodiment, correlating a sequence of requests with a message format also comprises satisfying one of the preconditions defined by the message semantics. For example, the correct message for an aircraft to transmit in order to communicate a sequence of update requests, q1, . . . , qn, made to its local information object may depend on whether the aircraft has 1) left the terminal gate, 2) completed takeoff, 3) landed on a runway, or 4) returned to a terminal gate. Thus, different request sequences can be specified for different circumstances that are captured by the preconditions. In one embodiment, update propagation function 114 determines whether one or more of the preconditions are satisfied by directly referencing one or more state variables of local information object 108. In one embodiment, update propagation function 114 determines whether one or more of the preconditions are satisfied by referencing the sequence of update requests being converted to messages.
In one embodiment, when a remote computer 124 coupled to communication link 118 receives an incoming message, an update reception function 122 applies a sequences of update requests, as defined by its own messaging model, to remote information object 120. Using message semantics from the messaging model, update reception function 122 correlates the incoming message to the associated sequences of update requests. In one embodiment, computer 102 further comprises an update reception function 116 that receives similar updates from an update propagation function 126 of the one or more remote computer systems 124 and applies the updates to the local information object 108 as described with respect to update reception function 122. In one embodiment, when a remote computer coupled to communication link 118 receives an incoming message, an update reception function 122 applies a sequence of update requests, as defined by its own messaging model, to remote information object 120.
In one embodiment, correlating an incoming message format with a sequence of requests also comprises satisfying preconditions defined by message semantics. In that case, in one embodiment, update reception function 122 selects a requests sequence q1, . . . , qn, for which one or more state variables of remote information object 120 satisfies the precondition. For example, the correct sequence of updates to apply to remote information object 120 upon receipt of a message from an aircraft may depend on whether one or more remote information object 120 state variables indicate that the aircraft has previously 1) left the terminal gate, 2) completed takeoff, 3) landed on a runway, or 4) returned to a terminal gate.
In one embodiment, update propagation function 114 determines which local information object 108 states to propagate based on one or both of information quality of service (IQoS) accuracy and freshness requirements, described by the '778 Application herein incorporated by reference. As described in the '778 Application, IQoS accuracy requirements control the selection of which states will be propagated from the local information object 108 to a destination information object 120 of the one or more remote computers 124. In one embodiment, a local information object 108 state must be propagated only if the change from the previously propagated state is large enough and the state has persisted for a sufficient time interval. The IQoS freshness requirement places a propagation delay bound Tp on the propagation time for propagating local information object 108 states to destination information object 120. In general, the larger the delay bound, the more flexibility communications network 118 has in allocating resources to propagate the local information object 108 states and the more resilient the replication function 106 is to temporary network unavailability.
When attempting to minimize network communications cost, it is important to know the cost of each message that might be used. This cost is generally determined by how a message's contents are represented as a sequence of bits for transmission, which also determines the message's length. For interoperability between computers, a message's encoding is also defined by the particular application-layer protocol enforced for communication network 118. Often, the message format and encoding are defined together. In other cases (as with ASN. 1), encoding rules are specified separately and different encoding rules can be used for the same message format.
In one embodiment of the present invention, when the messaging model identifies multiple ways to encode logged requests as a sequence of messages, update propagation function 114 chooses the least-cost encoding. Illustrated by the example provided in
In one embodiment, remote information object 120 is updated from initial state 310 to synchronized state 320 by update propagation function 114 sending a sequence of messages comprising messages m1, m2 and m3. In one embodiment, message m1 updates remote information object 120 from initial state 310 to updated state 312; message m2 updates remote information object 120 from updated state 312 to updated state 314; and message m3 updates remote information object 120 from updated state 314 to synchronized state 320.
In one embodiment, remote information object 120 is updated from initial state 310 to synchronized state 320 by update propagation function 114 sending a sequence of messages comprising messages m4, m5 and m6. In one embodiment, message m4 updates remote information object 120 from initial state 310 to updated state 314; message m5 updates remote information object 120 from updated state 314 to updated state 316; and message m6 updates remote information object 120 from updated state 316 to synchronized state 320.
In one embodiment update propagation function 114 evaluates the possible combinations of messages m1 to m6 and chooses the messages that require the least-cost to encode. In one embodiment, update propagation function 114 determines the least-cost encoding through a shortest path algorithm. For example, as opposed to encoding and sending messages m1 and m2 to reach state 314 from initial state 310, state 314 can be reached by encoding and sending the single message m4. Similarly, as opposed to encoding and sending messages m5 and m6 to update remote information object 120 from state 314 to synchronized state 320, synchronized state 320 can instead be reached by encoding and sending the single message m3. Applying a shortest path algorithm, update propagation function 114 would only propagate messages m3 and m4 because those messages provide the shortest path for updating remote information object 120 from initial state 310 to synchronized state 320.
As would be appreciated by one skilled in the art upon reading this specification, a shortest path algorithm is only one criteria which could be applied to determine the messages that require the least-cost to encode. For example, in one embodiment, based on the application-layer message formats defined by messaging model, message m4 might require a longer sequence of bits for transmission, or might require greater computing resources to encode, than message m1 and m2 combined. Thus using a least cost criteria based on either total bit length or encoding effort, update propagation function 114 would choose to send m1 and m2 under these circumstances, rather than m4.
Several means are available to implement one or more of the update propagation function, the update reception function, the request logging function and the log discussed with respect to the current invention. These means include, but are not limited to, digital computer systems, programmable controllers, or field programmable gate arrays. Therefore other embodiments of the present invention are program instructions resident on computer readable media which when implemented by such processors, enable the processors to implement embodiments of the present invention. As previously discussed, a messaging model of one embodiment of the present defines 1) valid application-layer message formats for protocol compliant messages, 2) the state space structure and update operations which apply to the local information object 108, 3) and message semantics which correlate the update operations with protocol compliant messages. In one embodiment, program instructions for one or more of the update propagation function, the update reception function, the request logging function and the log are generated by one or more automated software generation tools based on the messaging model.
Computer readable media include any form of computer memory, including but not limited to punch cards, magnetic disk or tape, any optical data storage system, flash read only memory (ROM), non-volatile ROM, programmable ROM (PROM), erasable-programmable ROM (E-PROM), random access memory (RAM), or any other form of permanent, semi-permanent, or temporary memory storage system or device. Program instructions include, but are not limited to computer-executable instructions executed by computer system processors and hardware description languages such as Very High Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL).
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
This application is also related to the following co-pending United States patent application filed on Nov. 3, 2004, which is hereby incorporated herein by reference: U.S. patent application Ser. No. 10/980,778 (attorney docket number H0008671-1633 entitled “Object Replication Using Information Quality of Service”) and which is referred to here as the '778 Application.
