Event notification over a communications network

1. A method for notifying one or more users of a present state of at least one property of an entity, the method comprising:

a) receiving a request message from a user over a first communications channel, the message containing information indicating at least one property of an entity in which the user is interested;

b) determining the present state of said at least one property;

c) determining an identifier of at least one second communications channel onto which future messages containing information relating to future changes of state of the at least one property of the entity will be transmitted; and

d) transmitting a reply message to the user, the reply message containing information indicative of the present state of the at least one property and of an identifier for each second communications channel;

wherein the determining in c) further comprises:

mapping the requested property to at least one communications channel onto which future messages which indirectly relate to the state of the property will be transmitted; and

wherein an identity of the at least one communications channel is used as the identifier.

2. A method for notifying one or more users of a present state of at least one property of an entity, the method comprising:

a) receiving a request message from a user over a first communications channel, the message containing information indicating at least one property of an entity in which the user is interested;

b) determining the present state of said at least one property;

c) determining an identifier of at least one second communications channel onto which future messages containing information relating to future changes of state of the at least one property of the entity will be transmitted; and

d) transmitting a reply message to the user, the reply message containing information indicative of the present state of the at least one property and of an identifier for each second communications channel;

wherein the determining in (c) further comprises:

checking whether the requested property has been previously requested by any user; and either

allocating a new identifier for the second communications channel if the property has not been requested previously; else

if the property has been requested previously, using the identifier previously allocated as the second communications channel identifier.

3. A method according to claim 2 , wherein the determining step c) further comprises:

mapping the requested property to a communications channel onto which future messages which directly relate to the state of the property that will be transmitted;

wherein the identity of the communications channel is used as the identifier.

4. A method according to claim 2 , wherein the second communications channel is an index channel, and the future messages to be transmitted thereon are index messages containing information relating to the identity of at least one further communications channel on which further messages relating to changes of state of the property are to be transmitted.

5. A method according to claim 2 , wherein the identifier of the second communications channel is an internet protocol multicast address.

6. A method according to claim 2 , wherein the determining in b) further comprises:

storing data relating to at least one property of at least one entity in a data store; and

searching the stored data to match the property indicated by the received message with at least one stored property if possible;

wherein if a match is found, the present state of the at least one matched stored property is determined as the present state of the requested property, else if no match is found, a null value is determined as the present state of the requested property.

7. A method according to claim 6 , wherein the null value is included in the reply message to the client as the present state of the requested property.

8. A non-transitory computer readable storage medium storing a computer program which when executed on a computer causes the computer to operate in accordance with the method of claim 2 .

9. A computer system comprising a non-transitory computer readable storage medium according to claim 8 .

10. A system for notifying one or more users of a present state of at least one property of an entity, said system comprising:

a) a message receiver for receiving a request message from a user over a first communications channel, the message containing information indicating at least one property of an entity in which the user is interested;

b) a processor arranged in use to:

i) determine the present state of said at least one property; and

ii) determine an identifier of at least one second communications channel onto which future messages containing information relating to future changes of state of the at least one property of the entity will be transmitted; and

c) a message transmitter arranged in use to transmit a reply message to the user, the reply message containing information indicative of the present state of the at least one property and of an identifier of each second communications channel;

wherein the processor is further arranged in use to:

iii) map the requested property to at least one communications channel onto which future messages which indirectly relate to the state of the property will be transmitted; and

wherein identity of each at least one communications channel is used as its identifier.

11. A system for notifying one or more users of a present state of at least one property of an entity, said system comprising:

a) a message receiver for receiving a request message from a user over a first communications channel, the message containing information indicating at least one property of an entity in which the user is interested;

b) a processor arranged in use to:

i) determine the present state of said at least one property; and

ii) determine an identifier of at least one second communications channel onto which future messages containing information relating to future changes of state of the at least one property of the entity will be transmitted; and

c) a message transmitter arranged in use to transmit a reply message to the user, the reply message containing information indicative of the present state of the at least one property and of an identifier of each second communications channel;

wherein the processor is further arranged in use to:

check whether the requested property has been previously requested by any user; and

either allocate a new identifier for the second communications channel if the property has not been requested previously; else

if the property has been requested previously, use the identifier previously allocated as the second communications channel identifier.

12. A system according to claim 11 , wherein the processor is further arranged in use to:

map the requested property to a communications channel onto which future messages which directly relate to the state of the property will be transmitted;

wherein the identity of the communications channel is used as the identifier.

13. A system according to claim 11 , wherein the second communications channel is an index channel, and the future messages to be transmitted thereon are index messages containing information relating to the identity of at least one further communications channel on which further messages relating to changes of state of the property are to be transmitted.

14. A system according to claim 11 , wherein the identifier of the second communications channel is an internet protocol multicast address.

15. A system according to claim 11 , wherein the processor is further arranged in use to:

store data relating to at least one property of at least one entity in a data store; and

search the stored data to match the property indicated by the received message with at least one stored property if possible;

wherein if a match is found the present state of the at least one matched stored property is determined as the present state of the requested property, else if no match is found a null value is determined as the present state of the requested property.

16. A system according to claim 15 , wherein the null value is included in the reply message to the client as the present state of the requested property.