INTERNET-DRAFT Jeff Bone, Activerse
Expires: Sept 1998 Lisa Dusseault, Microsoft
RVP Schemas
draft-dusseault-rvp-schema-00.txt
1. Status of this Memo
This document is an Internet-Draft. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF),
its areas, and its working groups. Note that other groups may
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Internet-Drafts are draft documents valid for a maximum of six
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in progress."
To learn the current status of any Internet-Draft, please check
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Shadow Directories on ds.internic.net (US East Coast),
nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or
munnari.oz.au (Pacific Rim).
2. Abstract
The RVP protocol [2] can be used to query properties of objects,
subscribe to certain kinds of events, and send instant messages
to objects. These objects are often users, but there are other
classes of objects as well.
A schema needs to be defined which applies to all kinds of RVP
objects, as well as more detailed schemas for the most commonly
used objects, users and groups.
The required properties for all RVP objects include common name
(Cn), schema type and access control list. The required
properties for a user object, which represents a single human
user of the system, include status, status message, email address
and directory server address. The required properties for a
group object, which represents a list of objects which may be
messaged all at once by messaging this group, include member-
count and owner.
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3. Contents
1. Status of this Memo.........................................1
2. Abstract....................................................1
3. Contents....................................................2
4. Overview....................................................3
4.1. The User Schema.......................................3
4.2. Group Schema..........................................3
5. Outline of a Schema.........................................4
5.1. Properties............................................4
5.2. Subscriptions Lists...................................4
5.3. Access Control lists..................................4
5.4. Timeouts..............................................4
5.5. Default Values........................................5
6. Schemas.....................................................5
6.1. Format of schema properties...........................5
6.2. All RVP Objects.......................................6
6.2.1. Schema-type property..............................6
6.2.2. Cn...............................................6
6.2.3. Link..............................................6
6.3. User Schema...........................................7
6.3.1. Status............................................7
6.3.2. Online-status.....................................7
6.3.3. Dir-entry.........................................8
6.3.4. V-Card............................................8
6.3.5. LastOn............................................8
6.3.6. LastOff...........................................8
6.3.7. Offline-msg.......................................9
6.3.8. Online-msg........................................9
6.3.9. Active-clients....................................9
6.4. Group Schema.........................................10
6.4.1. Online-members...................................10
6.4.2. Expires-offline..................................11
6.4.3. Multicast-addr...................................11
6.4.4. Max-Timeout......................................11
6.4.5. Total-members....................................12
6.4.6. Archive..........................................12
6.4.7. Owner............................................12
6.4.8. List-info........................................12
6.4.9. Recurses.........................................12
7. Extending Schemas..........................................13
7.1. Extending Existing Schemas...........................13
7.1.1. Storing private information in namespace.........13
7.2. Defining New Schemas.................................13
7.3. Auto-discovery of schemas............................14
8. REFERENCES.................................................14
9. Authors' Addresses.........................................14
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4. Overview
The RVP system is designed to provide dynamic information, not
static information. As such, all properties of objects are
dynamic, RVP-specific or very frequently queried by RVP users.
Some static properties such as the "directory address" property
for users and the "list-info" property for groups are required so
that users can find out where static information is supposed to
reside.
4.1. The User Schema
The user object is the most easily understood RVP object: it
represents a user. Some interesting properties of a user:
- They can have a status of offline, active, idle or busy.
- They may have a directory entry with static information.
- They may have a message intended for other users to see when
they are offline.
- They may have a message intended for other users to see when
they are online.
- They have an access control list (ACL) which defines who can
see the user object and who can message the user object.
- They have a subscription list (SL) which defines who wants to
receive instant messages which are sent to this user, and who
wants to receive notifications of things which change (certain
events) on the user object.
There must also be an access control list for each property which
defines who can read and who can write this property. There may
also be a timeout value for each property: for example, the
status of "active" times out to "offline" if the user does not
refresh the status property with a new timeout value.
Every entry in a subscription list contains the RVP address of
the subscriber, the address to send the notification to (the
callback, which may be a proxy address), and the kind of
notification they are interested in. Each entry in the
subscription list may also have a timeout entry and an access
control list. Some access control or other security mechanism
for the subscription list is required so that a malicious third-
party cannot cancel other people's subscriptions at will, but
subscribers can cancel their own subscriptions.
4.2. Group Schema
The next object to define is the group schema. A group is a list
of RVP objects which all receive an instant message sent to the
group. The group is an object itself because it is in many ways
similar to the user object.
- Users can post to the group just like a user, the server
forwards to the members of the group.
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- Users will want to know how many members of the group are
online, similar to knowing if a user is online.
Other aspects of groups are unique:
- Some groups will have a dynamic list of members who are all
online
- Some groups will have a static list of members, some of whom
may be online.
- Users may want to know what the total number of online &
offline members is
5. Outline of a Schema
5.1. Properties
Any property may have an ACL, default value, timeout value and
max timeout value.
5.2. Subscriptions Lists
Every entry in an SL may have an ACL and a timeout value. The SL
might have a max timeout value. The SL itself may also have an
ACL to decide who can GET the list, delete it, etc.
5.3. Access Control lists
Access Control Lists (ACL) are defined for DAV in [3]. These are
very flexible lists which can define access per user, per access
type. A user might be able to GET a property, but not SUBSCRIBE
to it or set it with PUT. ACL may define access by inclusion or
exclusion. ACLs are set on a property or object by sending an ACL
method message with a text/XML body. XML is flexible enough to
allow for additional access types and levels not foreseen here.
Every object and property may have an ACL. The ACL for the
object defines who send NOTIFY messages to the object, who can
SUBSCRIBE to messages from the object, who can use PUT to change
ACLs within the object, who can use GET to read ACLs within the
object, and who can DELETE the entire object.
For example, on a user object, SUBSCRIBE access is typically
granted to the user only, NOTIFY access to everybody except a few
people who hassle the user, and ACL/PUT/GET/DELETE access to the
user and their admin only.
An example of ACLs on a property: for the status property of a
user object, PUT would be restricted to the user, GET and
SUBSCRIBE would be granted to everybody but a few users, and
NOTIFY/DELETE would be meaningless and therefore might be
disallowed to everybody.
5.4. Timeouts
Timeout fields indicate the exact date and time when a property
or a list entry should expire. These fields are formatted
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according to ISO8601. The value of the timeout field may also be
"never".
For any property which can have a timeout, the server may also
maintain a maximum expiry duration. For example, if a user tries
to set the timeout on a subscription entry for longer than a day
away, the server may return a message which indicates that the
subscription was accepted but the timeout value was set to a
value of the server's choosing (specified in the return message).
When a list entry (ACL or SL) expires, the server should delete
the entry. It is not required that an implementation support
timeouts on ACL entries. It is required that an implementation
support timeouts on SL entries.
When a property expires, the server should set the property to
the default value.
5.5. Default Values
Properties which can expire (have timeout fields) should also
have default values. When the timeout is reached, the server
should set the property to the default value.
For example, the default value for the "status" field must be
"offline".
6. Schemas
6.1. Format of schema properties
Each schema property listed hereafter has several things
specified. The format of the property, the value, a description
of what the property is for, and an example are all pretty self-
explanatory.
The "required" bit specifies whether or not this must be
supported by a server implementation. Properties which are
supported by a server may still have a null value, and where that
is possible this is noted explicitly.
The "subscribable" information specifies whether the server
implementation must permit subscriptions to this property. "No"
means that an implementation is not required to support
subscriptions to this property, although an implementation may
support it anyway.
The "has" entry specifies what the server needs to have for each
property. All properties must have an Access Control List (ACL)
and may have to specify certain kinds of access, such as GET, PUT
and SUBSCRIBE, which are explicitly included in this
specification. Finally, the property may have to have a timeout
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(TO) and default value (DV). When a specific DV is required by
this specification, it is included. Items which are missing from
the "has" entry are optional.
6.2. All RVP Objects
All RVP Objects have an ACL and an SL. The SL is used to list all
subscriptions relating to that object, including subscriptions to
receive notifications sent to that object and subscriptions to
receive notifications when a particular property of the object
changes.
RVP objects can have content. For example, the authors envision
the content of an online document would be its text, and users
can subscribe to its properties. The issue has been raised that
user objects might have some sort of dynamic content to replace
some of their properties, but this issue has not been resolved
yet. In addition, all RVP Objects have the following properties:
6.2.1. Schema-type property
Format: string
Value: "user" | "group" | other defined schema
Has: ACL (put, get)
Required: Yes
Subscribable: No
Description: This allows the client to look up which scheme to
apply to the object. The client can then know what properties
are likely to be present.
Issue: We also need to define some way of showing that a new
schema is a sub-class of a known schema.
6.2.2. Cn
Format: String
Value: Common name of object
Has: ACL (put, get)
Required: Yes
Subscribable: No
Example: "Joe User"
6.2.3. Link
Format: String
Value: "REFER":[url] | "REFER-IM":[url] | "PROXY":[url] |
"LINK":[url] | null
Has: ACL (put, get) TO
Required: No
Subscribable: No
Example: REFER:rvp://host.com/joeuser
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Description: this is how another server or client can take over
control of the node. A detailed discussion of referral and
proxying can be found in the RVP draft [2]. Linking is much
simpler: the LINK value merely means that this object is only a
pointer to an object stored elsewhere, but which this server is
still responsible for.
6.3. User Schema
All user objects may have the following properties in addition to
properties required for all objects.
6.3.1. Status
Format: String
Value: "offline" | "online"
Has: ACL (put, get, subscribe), TO, DV = "offline"
Required: Yes
Subscribable: Yes
Description:
This indicates the user's online status. Online status is used
only when the user's has an open TCP connection to the server
which is responsible for the user's status, or if UDP is used
between client and server then this property must be refreshed
before the timeout (recommended 10 minutes) or the user will be
marked as "offline". If the server realizes that the connection
is lost or the property has not been refreshed, the server is
responsible for marking the user as offline. Thus,
online/offline status is determined by the client/server
connection. The exception is when a client wishes to be online
yet appear offline (invisible).
6.3.2. Online-status
Format: String
Value: "available" | "busy" | "idle"
Has: ACL (put, get, subscribe), TO, DV = "offline"
Required: Yes
Subscribable: Yes
Description:
Idle status is determined by the user's client. If the client
detects no input on the system hardware after a certain time, the
client should set this property on the server to "idle". The
client may change status back to "active" if new input is
detected, or the server may change status to "offline" if the
connection is dropped or the property times out.
Busy status is set by the user and can be taken to mean "do not
disturb". The user decides when they are busy, and when they are
no longer busy (active). The server can change the status to
"offline" if the connection is dropped or the property times out.
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Keeping these two status fields accurate, a job for clients,
servers and users, is important for a presence system. A user
should never appear as "available" if they have not touched their
computer (or other client) in over 15 minutes, or "online" if the
connection was lost.
6.3.3. Dir-entry
Format: String
Value: URL or blank
Has: ACL (put, get)
Required: Yes
Subscribable: No
Example: "URI:ldap://host.com:6666/o=3DABC%20Industries\,
c=3DUS??(cn=3DBJoe%20Users"
Description: this field points to the directory entry, typically
a LDAP URL but possibly a web page or other URL/URI, where static
information for the user can be found. Static information might
include phone number, email address, public key, etc.
6.3.4. V-Card
Format: String
Value: URL or blank
Has: ACL (put, get)
Required: No
Subscribable: No
Description: this field points to a location where a VCard can be
found for the user object.
6.3.5. LastOn
Format: date/time (RFC 1123)
Value: Date and time user last logged on
Required: No
Has: ACL (put, get)
Subscribable: No
Example: 06 Nov 1994 08:49:37 GMT
Description: This field records the last time the user became
active. The server should set this field. If multiple clients
are used, the server records the last time any client became
active.
6.3.6. LastOff
Format: date/time (RFC 1123)
Value: Date and time user last logged off (became "offline")
Required: No
Subscribable: No
Has: ACL (put, get)
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Description: If the user has multiple clients, the server records
the last time the user was completely offline (no online
clients).
6.3.7. Offline-msg
Format: MIME-type, typically text/plain
Value: Message intended for use when user is offline
Has: ACL (put, get, subscribe), TO, DV.
Required: no
Subscribable: Yes
Example: "I'm not logged in right now, please send email."
Description: This message will typically be like the voice mail
user messages or email OOF messages. We have not decided whether
or not the server must return the offline-msg in response to an
instant message sent when the user is offline.
6.3.8. Online-msg
Format: MIME-type, typically text/plain
Value: Message intended for use when user is online.
Has: ACL (put, get, subscribe), may also have TO/DV)
Required: no
Subscribable: Yes
Example: "I'm chatting in #foo if anybody wants to join me."
Description: This message will typically offer some information
about what the user is doing while online. This may help other
users decide how to get in touch.
6.3.9. Nickname
Format: String
Value: User's current nickname
Has: ACL (put, get)
Required: no
Subscribable: no
Description: Some group nodes MAY forward users' nicknames, if
provided, rather than users' real names. These group nodes will
typically be those provided for social interaction rather than
work. In cases where the user wishes to remain anonymous, the
client MAY send the nickname and not the Cn (common name) with an
instant message. The recipient of an "anonymous" message of this
type may refuse it. More details need to be worked out on the
use of nickname.
6.3.10. Active-clients
Format: string
Value: List of active client for this user, or null.
Has: ACL (put, get), TO, DV = null
Required: no
Subscribable: No
Description: Frequently users will have more than one client
connected. Clients should have types and may have simple
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identities. Each client type/identity is separated by a comma.
For example: "desktop=lisadu, desktop=lisa2, laptop=lisa,
cellphone=, pager=555-5555, PDA" In this example, the cellphone
identity is left blank because the user doesn't want their phone
number known that widely, and the PDA doesn't have an identity.
6.4. Group Schema
A group is similar to an email distribution list: it is a way of
redistributing instant messages to a list of users. A group is
structured similarly to users for ease of implementation.
Like any RVP object, the group object has a ACL and a SL. The SL
includes the list of users who wish to receive messages sent to
that group, and may also include users who wish to be notified
when a property of the group changes. The ACL for the group
object defines:
- who can send NOTIFY messages to the group
- who can GET the subscription list to see all members
- who can use ACL to change any of the ACLs under the group
object
- who can SUBSCRIBE to notifications sent to group
- who can DELETE the group object
Using PUT on the group object itself has no meaning.
An interesting aspect of groups is that in a dynamic system such
as RVP, group membership may also be very dynamic. For example,
a group such as "people looking for a ride home now" might have a
very dynamic member list. The server might have a maximum
timeout value on subscription list entries of twenty minutes
hence. Another group such as "members of this test team" might
have a very static member list, with timeout entries of "never".
In addition to the base object properties, the Group Schema has
the following properties.
6.4.1. Online-members
Format: Integer
Value: Number of online group members | NULL
Has: ACL (GET, SUBSCRIBE)
Required: Yes
Subscribable: no
Example: 42
Description: This value records the number of entities which are
currently online and subscribed to receive notifications sent to
the group, and should be maintained accurately by the server when
possible.
A value of NULL can mean several things:
- The number of online members is indefinite because there are
sub-groups
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- The number of online members is unknown because this is a
public group which may be fanned out by any proxy.
6.4.2. Expires-offline
Format: Boolean
Value: True | False
Has: ACL (Get, Subscribe)
Required: Yes
Subscribable: No
Description: This property, which should be GETable by all
potential members of the list, indicates whether the server
expires subscription list entries when the receiver is offline.
If TRUE, then offline recipients are dropped from the list. This
occurs if the response to a message from the publishing server is
an error/offline or no connection. If a server ever decides to
drop a member from a subscription list without an explicit
cancellation, the server should send a subscription cancellation
message to the client.
Note that this property also indicates to the client what the
client is supposed to do when it goes offline. The graceful
thing to do when expires-offline is TRUE is for the client to
cancel their subscription before going offline. Similarly, if a
proxy server is in the call-back path and the proxy server
becomes aware that the subscriber has gone offline, the proxy
server should cancel the subscription. The ability of the
publishing server to drop subscriptions from the list is supposed
to be used only when the graceful method fails.
6.4.3. Multicast-addr
Format: IP multicast addr
Value: Address which messages for this group are sent to
Has: ACL (Get, subscribe)
Required: No
Subscribable: no
Description: Large and public groups may support multicast:
messages to the group are sent to the multicast address. If a
multicast address is listed here and the client supports
multicast, the client should listen on the multicast address
rather than become a member of the group. Note that use of this
feature improves scalability but eliminates read ACLs.
6.4.4. Max-Timeout
Format: Integer
Value: Number of seconds
Has: ACL (GET, PUT)
Required: Yes
Subscribable: no
Example: 3600
Description: The max-timeout value should be queryable in most
cases, by most potential list members. A max-timeout of 0
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indicates "never": users can subscribe to this list without any
timeout on their subscriptions.
6.4.5. Total-members
Format: Integer
Value: Number of offline & online members | NULL
Has: ACL (get, put)
Required: Yes
Subscribable: no
Example: 58
Description: The value of this property is different from the
online-members property only for lists for which expires-offline
is false. The NULL value indicates the number of members is
unknown or uncertain.
6.4.6. Archive
Format: URL
Value: Location of archives | Null
Has: ACL (Get, put)
Required: No
Subscribable: no
Example: http://host.com/archives/rvpdisc
Description: if archives of this list are stored, this points to
them.
6.4.7. Owner
Format: URL
Value: Pointer to owner/moderator of list | Null
Has: ACL (Get,put)
Required: No
Subscribable: no
Example: rvp://host.com/joeuser
Description: This could be a RVP URL, mailto URL, web-page with
list of URLs, or other pointer to the owner/moderator of the
list.
6.4.8. List-info
Format: URL
Value: Pointer to more information about the list | Null
Has: ACL (Get, put)
Required: No
Subscribable: No
Example: http://host.com/protocols/rvpdisc/policies.html
Description: Any further information about the list, such as
requirements for getting onto the list, rules of behavior etc,
should be at the list-info URL or linked to from there.
6.4.9. Recurses
Format: Boolean
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Value: True | False
Has: ACL (GET, PUT)
Required: No
Subscribable: No
Description: If the server supports recursion of groups, and if
the value of "recurses" for a group is "true", then a message
sent to that group will also be sent to all child nodes of that
group. This allows large groups which don't have individual
members but which have child nodes, or groups which make up the
larger group. For example, the group
rvp://host.com/groups/rvpdisc
could have child nodes
rvp://host.com/groups/rvpdisc/newschemas
rvp://host.com/groups/rvpdisc/prot-methods
If recurses is set to true for rvpdisc, then both sub-groups
receive a message sent to rvpdisc.
7. Extending Schemas
7.1. Extending Existing Schemas
The user and group schemas are bound to be extended, with
properties for users such as "phone-status". Extensions to
existing, known schemas should always add, and not take away. If
this guideline is followed, then the extensions can all be listed
in this property after the base schema name, or in a new
property. Old clients which understand the "user" schema but not
any of the extensions can then ignore the extensions. The format
for listing extensions is undefined and suggestions are welcome.
When an extension to a schema is defined, it should be published
with a unique name.
7.1.1. Storing private information in namespace
This is entirely an optional feature. Servers may store
information in the namespace which is only intended for the
server and any of its users to get and set. For example, if a
user has a number of subscriptions which they wish to have active
every time they are online, then to minimize logon time the
server may allow the subscription information to be stored online
somewhere under the user's node in the namespace. When the user
logs on, the user may send a command to tell the user to activate
all the subscriptions stored in a particular location in the
local namespace.
7.2. Defining New Schemas
New schemas must be clearly justified and specified, published
and assigned a unique name.
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A new schema type of "automaton" has been suggested, with
potential sub-types of "gateway" and "archiver". This would
clearly identify automatic and special-purpose processes.
7.3. Auto-discovery of schemas
An unknown object can first be identified by the schema-type
property. However, the value of this field may not be known by
the client. It would be desirable to define a mechanism through
which the new schemas may be discovered on-the-fly.
This mechanism would have to communicate the name, format and
presence of SL/ACL/TO fields for each undefined property of the
schema. The name would have to be included so that a user could
decide whether to view the property, the format so that the
client could guess how to display the property, and the presence
of SL/ACL/TO information so that the client knows what may be
done with the property.
This mechanism could also be used to discover the nature of
extensions to known schemas.
8. REFERENCES
[1] S. Bradner, "Key words for use in RFCs to indicate
requirement levels," RFC 2119, Internet Engineering Task Force,
Mar. 1997.
[2] M. Calsyn, L. Dusseault and G. Mohr, "RVP: A Presence
Information Protocol", INTERNET-DRAFT <draft-calsyn-rvp-01.txt>,
March 1998
[3] Leach P. and Goland Y., "WebDAV ACL Protocol", INTERNET-DRAFT
<ftp://ftp.ietf.org/internet-drafts/draft-ietf-webdav-acl-
00.txt>, November 1997.
9. Authors' Addresses
Lisa Dusseault
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
EMail: lisadu@microsoft.com
Jeff Bone
Activerse, Inc.
1301 W. 25th St
Suite 500
Austin, TX 78705
Email: jbone@activerse.com
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