In distributed applications, a group of multiple processes cooperate by exchanging messages. It is critical to support the group of application processes with enough quality of service (QoS) including the ordered delivery of messages. The delay time and the message loss ratio are significant QoS parameters. In Internet applications, the delay time and the loss ratio are significantly different in different communication channels. The authors define a novel causality named /spl Delta/*-causality among the messages to hold in the world-wide environment. They discuss how to transmit messages to the destination processes and how to resolve message loss and delay supporting the /spl Delta/*-causality given the requirements of delay time and message loss ratio.

Distributed applications are modelled in an object-based model like CORBA. Here, the system is a collection of objects. The objects are manipulated only through operations supported by themselves. The purpose-oriented model is proposed where an access rule shows for what each subject s manipulates an object o by an operation t of o so as to keep the information flow legal. The purpose of s to access o by t is modelled to be what operation u of s invokes t to manipulate o. That is, the purpose-oriented access rule is specified in the form (s:u, o:t). In the object-based system, on receipt of a request op from an object o/sub 1/, an object o/sub 2/ computes op and then sends back the response of op to o/sub 1/. Here, if the request and the response carry data, the data in o/sub 1/ and o/sub 2/ is exchanged among o/sub 1/ and o/sub 2/. Furthermore, the operations are nested in the object-based system. Even if each purpose-oriented rule between a pair of objects satisfies the information flow relation, some data in one object may illegally flow to another object through the nested invocation of operations. In this paper, we discuss what information flow is legal in the nested invocations in the purpose-oriented model of the object-based system.

In group communications, larger computation and communication overhead are considered to causally order all the messages transmitted in the network. Transactions in clients manipulate objects in servers by sending read and write requests to the servers. In this paper, we define significant messages by using the relation among the transactions. We newly propose an object vector to causally order only the significant messages. The scheme of the object vector is invariant in the change of the group membership. We also show a TBCO (transaction-based causally ordered) protocol which adopts the object vector, by which the number of messages to be causally ordered are reduced.

In distributed applications, a group of multiple processes cooperate by exchanging multimedia messages. It is critical to support the group of application processes with enough quality of service (QoS) in addition to the ordered delivery of messages. The delay time and the message loss ratio are significant QoS parameters. In the Internet application, the delay time and the loss ratio are significantly different in different communication channels. We define a novel causality named /spl Delta/*-causality among the messages to hold in the world-wide environment. We discuss how to transmit messages to the destination processes and how to resolve the message loss and delay supporting the /spl Delta/*-causality given the requirements of delay time and message loss ratio.

In distributed applications, a group of multiple objects are cooperating to achieve some objectives. An object is modeled as a pair of data structures and operations. Each object is manipulated through an operation supported by the object and then the operation may further invoke operations of other objects, i.e., nested operations. The purpose-oriented access rules indicate which operation on each object can invoke operations of other objects. The information flow among the objects occur if the requests and responses of the operations carry some data. Only the purpose-oriented access rules which imply the legal information flow are allowed. We discuss how to test the access rules if the information flow occurring in the nested invocation of the operations is legal.

This paper proposes a novel algorithm for taking checkpoints and rolling back the processes for recovery in asynchronous distributed systems. The algorithm has the following properties: (1) multiple processes can simultaneously initiate the checkpointing; (2) no additional message is transmitted for taking checkpoints; (3) a set of local checkpoints taken by multiple processes denotes a consistent global state; (4) multiple processes can initiate simultaneously the rollback recovery; (5) the minimum number of processes are rolled back; and (6) each process is rolled back asynchronously. The number of messages for rolling back the processes is O(l) where l is the number of channels. Therefore, the system is kept highly available by the algorithm presented.

In distributed applications, a group of multiple objects are cooperated. On receipt of request messages, the objects send back the responses. The kinds of group communication protocols discussed so far, support the reliable and ordered delivery of messages at the network level. Only messages to be ordered at the application level, not necessarily all messages, are required to be causally delivered in the required order. The state of the object depends on in what order the requests are computed and the responses and requests are transmitted. In this paper, we would like to define the significant precedence order of messages based on the conflicting relation among the requests. We would like to discuss a protocol which supports the significantly ordered delivery of request and response messages.

In distributed applications, a group of multiple application processes have to send and receive multimedia messages by using the high-speed network. The multimedia message at the application level is decomposed into multiple smaller packets which are transmitted in the communication system. In this paper, we discuss the atomic and ordered delivery of messages at the application level rather than the system level. In some multimedia applications, the application processes do not mind if some packets are lost and in what order packets from different processes are received. The application process specifies the minimum receipt ratio /spl epsiv/ (/spl les/1) showing how many percentages of whole data in each message the destination processes have to be received at least. The communication system delivers the packets to the destinations in the group so as to satisfy the receipt ratio /spl epsiv/. The protocol is based on the fully distributed control scheme, i.e. no master controller.

In distributed applications, a group of application processes is established and the processes in the group communicate with one another, i.e. intra-group communication. Here, messages have to be reliably and causally delivered to all the destinations. In addition, the processes send messages to any subset of the group at any time. This paper presents an intra-group communication protocol which provides the group of application processes with the selective and causally ordered (SCO) delivery of messages. The SCO protocol is based on the fully distributed control scheme, i.e. no master controller and uses the high-speed one-to-one network where messages may be lost due to the buffer overrun and congestion.

In group communication, multiple processes have to receive messages in some order. We discuss a group communication protocol which supports a selective total-ordered (ST) and atomic delivery of messages to the destinations in a group of processes interconnected by a high-speed channel, where the processes may fail to receive messages due to the buffer overruns. That is, each process receives messages destined to it in the sending order and any two common destinations of messages are received in the same order. Its execution is controlled in a distributed scheme, i.e. no master controller.>

Distributed application systems require group communications among multiple processes. In the group communication, it is important to discuss in what order each process in the group can receive messages. The paper presents a causally ordering group communication (CO) protocol which provides the same causal ordering of messages for all the processes in the group. In the CO protocol, the messages received are causally ordered by using the sequence numbers of the messages. The CO protocol is based on the fully distributed control scheme, i.e. no master controller, and uses high-speed networks where each process may fail to receive messages due to the buffer overrun. Furthermore, the CO protocol provides asynchronous data transmission for multiple processes in the group.