]> Validation of Locations Around a Planned Change
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ART ecrit This document defines an extension to the Location to Service Translation (LoST) protocol (RFC5222) that allows a LoSR server ti notify a client of planned changes to the data. This extension is only useful with the validation function of LoST. It is beneficial for LoST validation clients to be aware of planned changes, as records that previously were valid may become invalid at a known future date, and new locations may become valid after the date. This extension adds an element to the <findService> request: a date that allows the LoST client to request that the server perform validation as of the date specified. It adds an optional Time-To-Live element to the response, which informs clients of the current expected lifetime of a validation. It also adds a separate interface to the LoST server that allows a client to poll for planned changes. Additionally, this document provides a conventional XML schema for LoST, as a backwards compatible alternative to the RelaxNG schema in RFC5222.
Introduction Validation of civic locations involves dealing with data that may change over time. A typical example is when a portion of a county or district that was not part of a municipality is "annexed" to a municipality. Prior to the change, a Presence Information Data Format Location Object (PIDF-LO) specifying a civic location in the affected area would have a blank A3 element, or would contain some other value; after the change, a PIDF-LO specifying the same location would contain an A3 element set to the name of the municipality that annexed that part of the county/district. This kind of annexation has an effective date and time (typically 00:00 on the first or last day of a month), known in advance. Other kinds of changes may also occur, and these will almost always also have an effective date that is known in advance. Records in a LIS must change around these kinds of events. The old record must be discarded, and a new, validated record must be loaded into the LIS. It is often difficult for the LIS operator to know that records must be changed around such events. There are other circumstances where locations that were previously valid become invalid, such as a street renaming or renumbering event. Using validation, the only way for a LIS to discover such changes is to periodically revalidate its entire database. Of course, this does not facilitate timely changes, is not coordinated with the actual change event, and also adds significant load to the LoST server as well as the LIS. Even if re-validation is contemplated, the server has no mechanism to control, or even suggest the time period for revalidation. This extension allows a LoST client to obtain from the LoST server sets of locations which may change. It makes use of "partial location information" which is a set of location elements and values that, when compared against the client's location records, identify which of the clients records may change as a result of the planned change. A set of such partial locations is termed a "ChangeSet". ChangeSets have an ID, and a date when the change is effective. IDs are ordered. The planned change interface is a REST/JSON interface that allows the client to poll the server using the last ID that it obtained from that server. The response to the poll is a list of all the newer planned changes the server knows about beyond the ChangeSet whose ID was included in the poll. The ID for the last ChangeSet in the returned list will be used by the client for the next poll. When a LIS receives a new ChangeSet, it may prepare one or more new records so that, at the precise planned event date and time, it may insert the new records into in its active database and delete the old records. As part of preparing the new records in advance of the change, the LIS may use the "asOf" date component of this extension to perform a LoST validation of the new record as of the effective date. In its response, the LoST server may include a new "expires" element that expressly states when the location should be re-validated, rather than blindly revalidating every address on a schedule chosen by the client. The "asOf" date component of this extension in a <FindService> request allow a LIS to be prepared for and smoothly transition to planned changes. The polling mechanism allows a LIS to be alerted to planned changes, while the "asOf" date allows the LIS to verify the validity of locations before they become active. Unplanned changes will occur, and periodic revalidation can still be used to maintain the data in the LIS. However, the LoST server should be able to influence the rate of such revalidation. For this purpose, this extension adds a "expires" element to the <findServiceResponse> which provides advice from the server to the LIS of when validation is suggested. There are quite a few implementations of LoST. Experience with these implementations indicates that the RelaxNG schema is very difficult to deal with, both because many commonly used development tools don't support it, and development staff is often unfamiliar with it. Informal alternative schemas have been circulated, which is undesirable as they may not be in conformance with the RelaxNG schema in . This document provides an XML schema that replaces the RelaxNG schema. It can be used by any implementation interchangeably with the RelaxNG schema.
Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. "Server" in this document refers to the LoST server and "Client" is the LoST client, even when the server is performing an operation on the client.
Planned Change Poll Interface This document defines a new interface to the LoST server. The interface has three entry points. Entry point one, Versions, returns the current version(s) the interface supports. This allows the interface to evolve over time. Entry point two, PlannedChangePoll, is a poll. The poll returns a list of changeSetIds which identify ChangeSet objects. The third, GetChangeSet, accepts a changeSetId and returns the ChangeSet object which contains the identifier (changeSetId), a date (changeSetEffective) and an array of partial locations. A partial location is an array of location information element name and value pairs. The client compares the location elements with its records. For each of the clients records where all of the location elements provided in the partial location have the same values as those in the partial location, that client record may be affected by the planned change. The client's records may have other location elements, but those are not considered in the comparison. So, for example, a partial location may have a Country, A1, A2, A3 and A4 location elements, which means that any address with that Country, A1, A2, A3 and A4 values may be affected by the planned change regardless of street name and number. As another example, a partial location with Country, A1, A2, A3, A4, RD and POD but not HN means any address number on the specified street. The changeSetId is string, which the server maintains as an ordered list of changeSetIds. The id itself may not show the ordering. For example, it could be a hashed timestamp, or a hashed sequence number. Given a changeSetId returned by it in a prior poll, the server can identify which ChangeSets it has that come after, in order, after the one with the proffered changeSetId. A new client does not know any ids, or a client may lose the id that it had. The client would poll omitting the changeSetId in the poll query, and in the response, the server returns all the ChangeSets it knows about. The effective date of a ChangeSet returned by the server need not always be in the future. Tardy clients may not keep up. On the other hand, the server is not obligated to keep change sets whose changeSetEffective date has passed for more than some arbitrary time. A 12 month time period may be appropriate for a server whose service area doesn't have many changes, where a 3 month time period may be needed in a fast changing service area where many changes occur regularly. A tardy client in a fast changing environment may receive a large number of ChangeSets in response to a poll. Polls are expected every few minutes. A new client omits the ID in its first poll, and the server responds with all the changeSetsIds that it knows about. Thereafter, the client retains the last changeSetId in its most recent poll and uses that in the next poll. If the response to that poll is no changeSetIds, it means the changeSetId the client has is the latest change the server knows about, and that same changeSetId will be used in subsequent polls until the server returns a new one. The version mechanism returns a list of versions of the web service it supports. This document describes version 1.0. Versions are described as a major version and a minor version, where major and minor versions are integers. A backwards compatible change within a major version MAY increment only the minor version number. A non-backwards compatible change MUST increment the major version number. To achieve backwards compatibility, implementations MUST ignore any object members they do not implement. Minor version definitions SHALL only add objects, non-required members of existing objects, and non-mandatory-to-use functions and SHALL NOT delete any objects, members of objects or functions. This means an implementation of a specific major version and minor version is backwards compatible with all minor versions of the major version. The versions mechanism returns an array of supported versions, one for each major version supported, with the minor version listed being the highest supported minor version. When versions are written or used as a string, the major version is first and separated from the minor version with a period. For example major version 3, minor version 2 would be written as "3.2"
<plannedChange> element This document defines a new element in the <findService> request called "zHxogxRv8SoYre6p1feA7odJF7a0SlwKhPwv". This element contains an attribute: 'asOf' which contains a date and time in dateTime format with a required timezone. The server validates the location in the request as of the date and time specified, taking into account planned changes. This allows a client to verify that it can make changes in the LIS commensurate with changes in the LoST server by validating locations in advance of a change.
"expires" in Response This extension adds the 'expires' element to the <findServiceResponse>. The 'expires' element contains a date and time after which the client may wish to revalidate the location at the server. A server MAY add this attribute to the response if validation is requested. This element takes the form of the 'expires' attribute pattern of , which allows the values "NO-CACHE" or "NO-EXPIRATION" to be returned instead of a dateTime value. However, for the 'expires'; attribute "NO-CACHE" has no meaning and MUST NOT be returned. "NO-EXPIRATION" means the server does not have a suggested revalidation period. Selecting a revalidation interval is a complex balancing of timeliness, server load, stability of the underlying data, and policy of the LoST server. Too short, and load on the server may overwhelm it. Too long and invalid data may persist in the client for unacceptable lengths of time. The polling mechanism provides timely notice to coordinate changes, but even with it, it is often advisable to revalidate data eventually. In areas that have little change in data, such as fully built out, stable communities already part of a municipality, it may be reasonable to set revalidation periods of 6 months or longer, especially if the URI mechanism is widely deployed at both the server and the clients. In areas that are quickly growing, 20-30 day revalidation may be more appropriate even though such revalidation would be the majority of the traffic on the LoST server. When a planned change is made, typically the expires value for the affected records is lowered, so that revalidation is forced soon after the change is implemented. It is not advisable to set the expiration precisely at the planned change time if a large number of records will be changed, since that would cause a large spike in traffic at the change time. Rather, the expiration time should have a random additional time added to it to spread out the load.
Replacement XML schema This schema is an alternative to The Relax NG schema in . Future extensions to LoST are expected to use this schema as the base for the extensions, rather than the Relax NG schema. Existing extensions described using the Relax NG schema continue to be valid. Exception pattern. type="basicException"/> Any element not in the LoST namespace. A wildcard pattern for including any element from any other namespace. A wildcard pattern for including any element from any other namespace. A point where future extensions (elements from other namespaces) can be added. ]]>
Extension XML Schema This schema provides the extension to the prior section schema for planned changes: ]]>
plannedChangePoll Interface Description
Security Considerations As an extension to LoST, this document inherits the security issues raised in . The server could be tricked into storing a malicious URI which, when sent the revalidateLocation object could trigger something untoward. The server MUST NOT accept any data from the client in response to POSTing the revalidateLocation. The server is subject to abuse by clients because it is being asked to store something and may need to send data to an uncontrolled URI. Clients could request many URIs for the same location, for example. The server MUST have policy that limits use of this mechanism by a given client. If the policy is exceeded, the server returns the <uriNotStored> warning. The server MUST validate that the content of the 'uri' attribute sent is syntactically valid and meets the 256 bytes limit. When sending the <revalidateLocation> object to the URI stored, the server MUST protect itself against common HTTP vulnerabilities. The mutual authentication between client and server is RECOMMENDED for both the initial <findServiceRequest> operation that requests storing the URI and the sending of the <revalidateLocation> object. The server should be well known to the client, and its credential should be learned in a reliable way. For example, a public safety system operating the LoST server may have a credential traceable to a well known Certificate Authority known to provide credentials for public safety agencies. Clients may be operated by local ISPs or other service providers that can reasonably obtain a good credential to use for the server side of the LoST server's POST transaction using the URI. Where the loST server does not recognize the client, its policy MAY limit the use of this feature beyond what it would limit a client it recognizes.
IANA Considerations
Replacement XML Schema Registration The XML Schema is found in .
Planned Change Extension XML Schema Registration LoST Planned Change Namespace

Namespace for LoST

urn:ietf:params:xml:ns:lostPlannedChange1

See RFC????.

END ]]> The XML Schema is found in .
Normative References A Presence-based GEOPRIV Location Object Format This document describes an object format for carrying geographical information on the Internet. This location object extends the Presence Information Data Format (PIDF), which was designed for communicating privacy-sensitive presence information and which has similar properties. [STANDARDS-TRACK] LoST: A Location-to-Service Translation Protocol This document describes an XML-based protocol for mapping service identifiers and geodetic or civic location information to service contact URIs. In particular, it can be used to determine the location-appropriate Public Safety Answering Point (PSAP) for emergency services. [STANDARDS-TRACK] Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.