This is an old revision of the document!
Proximity is a filter object that contains a “function” that determine whether or not a user is proximate. There are several predefined functions:
Other functions can be defined as combinations of existing functions by means or combinators: and, or, not.
Proximities translate these events into addUser / removeUser events to be processed by flocks. To process these events, flocks register themselves on their dependent proximity.
Programmers can make customised proximity functions. In order to aid the programmer in this tasks we have defined some auxiliary functions and constructors. In the code shown bellow we make a proximity function that maps the domain of persons onto the set of people who are both female and friends in the proximity. The first step in the code is to create the female proximity. This is constructed by making a profile proximity. The first parameter is the flockr and the second is a lambda which expects a profile. This lambda must return a boolean value and indicates that the matched profile is in the proximity or not. In this case we check that the sex of the profile is female. The second proximity is a predefined one and only passes friends that are in the neighbourhood. The last step is to combine the two defined proximity's into one. As we only want to show those friends in the neighbourhood who are female we combine them by making use of a and proximity.
def femaleProximity := makeDoesProfileMatchProximity(flockr1 , { |profile| profile.sex == "FEMALE" }); def friendProximity := makeIsFriendProximity(flockr1); def friendAndFemaleProximity := makeAndProximity(femaleProximity, friendProximity);
An ad hoc RETE-network. Events are triggered by:
joined(uid,flockr)
/ left(uid,flockr)
changed(uid,flockr,updatedProfile)
friendAdded(uid,flockr)
/ friendRemoved(uid,flockr)
These events are received by the local flockr user object and propagated to all local proximities. Proximities translate these events into addUser / removeUser events to be processed by flocks. To process these events, flocks register themselves on their dependent proximity.
Alternative implementation of the RETE-network, maybe we can start from the oo matching that Tom implemented, so that Proximity functions are templates. For example:
def flockrTemplate := template: { def name := *; // wildcard, can be anything def age := constraint: { _ < 25 }; // must be younger than 25 def address := template: { def street := *; //any street,but street name must be filled def city := "Brussel"; // city must equal this string }; def greet(); // person must have a greet method } taggedAs: [ Flockr ]; // object must be tagged as a Flockr
Note of Tom: maybe too complex to use the templates, because we are not going to match on type tags or methods (only on state). We can simply compile proximities into boolean expressions of the form (ATTR OP VAL)
It appears that some proximities are mandatory, e.g. a composite proximity requires at least the isFriend / isNearby / wasNearby proximity functions. The doesProfileMatch proximty is optional. So we have the following constraints on proximities: