RFC1431 - DUA Metrics (OSI-DS 33 (v2))

Network Working Group P. Barker

Request for Comments: 1431 University College London

February 1993

DUA Metrics

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard. Distribution of this memo is

unlimited.

Abstract

This RFCis being distributed to members of the Internet community in

order to solicit their reactions to the proposals contained in it.

While the issues discussed may not be directly relevant to the

research problems of the Internet, they may be interesting to a

number of researchers and implementers.

This document defines a set of criteria by which a DUA

implementation, or more precisely a Directory user interface, may be

judged. Particular issues covered include terminal requirements;

style of interface; target user; default object classes and attribute

types; use of DAP; error handling. The focus of the note is on

"white pages" DUAs: this is a reflection of the current information

base. Nevertheless mUCh of the document will be applicable to DUAs

developed for other types of Directory usage.

Please send comments to the author or to the discussion group <osi-

ds@CS.UCL.AC.UK>.

Table of Contents

1. Overview................................................ 2

2. General Information..................................... 3

3. Conformance to OSI Standards............................ 5

3.1 Directory protocols.............................. 5

3.2 Protocol stacks.................................. 5

3.3 Schema .......................................... 5

3.4 DIT structure .................................. 5

4. Conformance to Research Community Standards............. 6

5. The General Style of the DUA............................ 6

6. Schema.................................................. 7

6.1 Object Classes and Attribute Types............... 7

6.2 DIT structure.................................... 8

7. Entering queries........................................ 9

8. Strategy for locating entries........................... 9

9. Displaying results...................................... 10

10. Association Handling.................................... 11

11. Suitability for management.............................. 12

12. Query Resolution........................................ 13

13. International Languages................................. 16

14. User Friendliness....................................... 16

15. Operational Use......................................... 17

16. Security Considerations................................. 19

17. Author's Address........................................ 19

1. Overview

The purpose of this document is to define some metrics by which DUA

products can be measured. It should be first be noted that the use

of the term "DUA" is rather misleading. There is an assumption here

that the DUA is implemented correctly and is able to "talk" valid

X.500 protocol: this is a sine qua non. Instead, this document seeks

to draw out the characteristics of Directory user interfaces.

However, the term DUA is persisted with as it is used by most people

when referring to Directory user interfaces. The format of these DUA

metrics is essentially a questionnaire which extracts a detailed

description of a user interface. DUAs come in very different forms.

Many make use of windowing environments, offering a "high-tech" view

of the Directory, while others are designed to work in a terminal

environment. Some interfaces offer extensive control over the

Directory, and thus may be well-suited to Directory managers, while

others are aimed more at the novice user. Some interfaces are

configurable to allow searches for any attribute in any part of the

DIT, while others lack this generality but are focussed on handling

the most typical queries well. In many ASPects, it is almost

impossible to say that one DUA is better than other from looking at

the responses to question in this document. A flexible management

tool will be better for management than a DUA aimed at servicing

simple look-ups, and vice-versa. Furthermore, in other areas, there

are several radically different approaches to a problem, but it is

not as yet clear whether one approach is better than another. One

example of this is the extent to which a DUA provides an abstraction

of the underlying DIT hierarchy, either emphasising the world as a

tree or trying to conceal this from the user.

However, other aspects, such as whether the DUA can actually find the

entries required, and if so, how quickly, can be directly measured in

some way. Throughout this document, some of the questions posed are

annotated with a square-bracketed points score and an eXPlanation as

to how the points should be allocated. For example, a question might

be appended with "[2 if yes]", indicating score 2 points for an

affirmative answer to that question. These points scores should be

collated in Table 1 at the end of the document, and this table

constitutes a measure of the DUA. The metrics are on a section by

section basis, which should help the reader who is seeking, for

example, a DUA with good management capabilities which runs on a wide

variety of platforms, to focus on the critical aspects of a DUA for

the particular requirement.

2. General Information

This section contains general information about the implementation

under discussion.

1. Name of the implementation ......................................

2. Version number of the DUA described in this document ............

3. Are further versions planned? [3 if yes] .......................

4. Name and address of supplier or person to contact ...............

....................................................................

5. Describe the hardware and software platforms on which the DUA will

run. Some DUAs are split into a user interface part, and a DUA

server part, communicating by means of a protocol. If the DUA is

of the type where the DUA protocol machinery and user agent are

implemented in a single process, complete only the user interface

section, and indicate "n/a" for the DUA server and

communications protocol questions.

(a) User interface part [1 per platform, up to a maximum of 4]

i. Hardware (If appropriate, can summarise as, for example,

ii. O/S (state version if critical)

A. UNIX (be sure to indicate which flavour - e.g., SYSV,

BSD, SUNOS, etc) ....................................

........................................................

B. VMS) ................................................

C. MS-DOS ..............................................

D. MS-Windows ..........................................

E. Macintosh ...........................................

F. Other) ..............................................

(b) DUA server part (or n/a) ....................................

i. Hardware (If appropriate, can summarise as, for example,

"generic UNIX platform", or "386 PC") ...............

ii. O/S (state version if critical)

A. UNIX (be sure to indicate which flavour - e.g., SYSV,

BSD, SUNOS, etc) ....................................

B. VMS) ................................................

C. MS-DOS ..............................................

D. Macintosh ...........................................

E. Other) ..............................................

iii. How does the user interface communicate with the DUA

server?

A. Directory Assistance Service, as described in RFC1202

........................................................

B. DIXIE protocol, as described in RFC1249 .............

C. LDAP protocol, as described in Internet Draft OSI-DS

D. Other ...............................................

supplied with the operating system or with the DUA software

itself. Examples might include X.500 DAP libraries, or

communications software .....................................

6. Is the software free? If the DUA needs other packages, are these

also freely available? [3 if completely free] ..................

....................................................................

3. Conformance to OSI Standards

3.1 Directory protocols

7. Please list all conformance testing work applied to the DUA

implementation (here the term DUA is used correctly in the sense

of the DUA protocol machinery) [2 if any conformance work has been

done] ...........................................................

....................................................................

3.2 Protocol stacks

For the next two questions, [2 per stack supported for up to 4

stacks]

8. Which of the following transport and network layer protocols does

the DUA support:

(a) TP.x over CONS (state transport class) ......................

(b) TP.4 over CLNS ..............................................

9. Does the DUA support other transport and "network" layer

protocols?

(a) TP.x over RFC1006 over TCP/IP (state transport class) .......

(b) TP.x over X.25(1980) (state transport class) ................

10. Does the DUA also run over any lightweight stack? If so, describe

it with reference to the OSI seven layer model [3] ..............

....................................................................

3.3 Schema

11. Does the DUA support the full schema in X.520 and X.521 (y/n)?

(Omissions should be described in response to a later question) [2

for full schema support] ........................................

3.4 DIT structure

12. Does the DUA only follow object class hierarchies which conform to

the suggested DIT structure in X.521?............................

4. Conformance to Research Community Standards

The COSINE and Internet Directory Pilots have agreed a set of

extensions to the standard, which make for a more cohesive pilot.

This section is about conformance to these extensions.

13. Does the DUA fully support RFC1274, "The COSINE and Internet

X.500 Schema" (y/n)? (Omissions should be described in response

to a later question) [2 for full support] .......................

14. Can the DUA handle referrals whose network addresses conform to

RFC1277, "Encoding Network Addresses to support operation over

non-OSI lower layers"? [2 if yes] .............................

15. Does the DUA handle the Distinguished Name string syntax described

in OSI-DS 23, "A String Representation of Distinguished Names"

[2 if yes] ......................................................

....................................................................

16. Does the DUA use the user-friendly naming query resolution

described in OSI-DS 24, "Using the OSI Directory to achieve User

Friendly Naming" [2 if yes] ....................................

17. Does the DUA make use of the Quality of Service schema extensions

described in OSI-DS 15, "Handling QOS (Quality of service) in the

Directory" [2 if yes] ..........................................

5. The General Style of the DUA

18. Is this a "white pages" interface, designed to give Access to

information about people within organisations? If not, state the

types of information at which this interface is targetted .......

....................................................................

19. If this is a white pages DUA, who is it principally designed to

serve? Indicate more than one of the following categories if

appropriate (but please do not fill in so may categories as to

hide due emphasis): [mark allocated should be the highest for any

single classification]

(a) The ordinary user, who has no understanding of X.500, the

hierarchical DIT, the state of advancement of the pilot, etc.

[10] ........................................................

(b) A secretary who wants to do telephone or room number look-ups

within their department or organisation [8] .................

network services [6] ........................................

(d) An organisation's (or department's) data manager [4] ........

(e) A Directory system manager [2] ..............................

20. Which best describes the use the DUA makes of the user's terminal?

(a) Scrolling, line-mode interface ..............................

(b) Full screen, "vt100" style interface ......................

(d) MS-Windows ..................................................

(e) Macintosh ...................................................

(f) Other .......................................................

21. Does the DUA tend to emphasise or de-emphasise the DIT hierarchy?

....................................................................

22. Describe the interface in your own terms (up to about 50 Words)

....................................................................

6. Schema

6.1 Object Classes and Attribute Types

Some DUAs are tightly focussed on answering particular queries: for

example, white pages look-ups for information about people. Others

offer more general capabilities. Please answer this question

accordingly.

23. If the DUA has a tight focus, state:

(a) The target object classes ...................................

................................................................

(b) The default attribute types .................................

................................................................

answered as, for example, "all barring photo and audio", or

as a list of supported attribute types ......................

................................................................

24. If the DUA has more general capabilities, state:

(a) State any object classes in X.521 which cannot be searched for

................................................................

(b) State any object classes in RFC1274 which cannot be searched

for..........................................................

................................................................

(d) State any attributes in RFC1274 which cannot be displayed....

................................................................

6.2 DIT structure

25. DUAs often have a default object class hierarchy (e.g., it might

assume countries at the root of the DIT, organisations immediately

under countries, and people somewhere under organisations.

Describe the type of hierarchy which the DUA most closely accords

to:

(a) Rigid .......................................................

(b) Rigid, but several hierarchies supported ....................

................................................................

(d) Default hierarchy offered, but DUA fully flexible ...........

(e) No default hierarchy, DUA fully flexible ....................

26. If a default hierarchy is offered, please describe it ...........

....................................................................

27. State any hierarchies, which are valid according to X.521's

suggested DIT structure, but which cannot be queried (exclude

hierarchies which cannot be queried because the DUA does not query

for entries of particular object classes) .......................

....................................................................

7. Entering queries

The term "querying" is used here as a generic term for finding an

entry, whether it be as a simple look-up, or the prelude to a

modification operation.

28. Which best describes the query entry style?

(a) Form filling (user responds to a set of prompts) ............

i. Query specified first, then resolved ....................

ii. Query entry and resolution mixed ........................

iii. Both modes possible .....................................

(b) Queries entered as "user-friendly names" ..................

searching and selecting .....................................

(d) Other (please describe) .....................................

................................................................

8. Strategy for locating entries

A number of strategies are employed by DUAs to find the entry the

user is looking for. These have implications for user-friendliness

and performance. For example, an interface which makes extensive use

of search operations may be Excellent at finding entries, but at the

cost of being intolerably slow.

29. Which of the following strategies most closely accords with the

behaviour of the DUA?

(a) The DUA always uses search operations to find entries .......

(b) The DUA offers users a list of entries, and invites the user

to select from the list .....................................

exactly right) ..............................................

(d) The DUA tries read operations first, then searches for

something similar if no entry can be found ..................

(e) The DUA tries read operations first, then offers a list of

possible entries if no entry can be found ...................

(f) User explicitly controls the X.500 operation which is invoked

(g) Other. Please describe......................................

................................................................

30. Does the DUA allow a user to "list" (either by the list

operation or by a single level search operation) all the child

entries of a node (notwithstanding administrative limits)? .....

31. Does the DUA follow aliases? ...................................

If so, does it do so:

(a) Always? ....................................................

(b) Optionally? ................................................

32. Will the DUA optionally follow links to other entries by using

attributes such as seeAlso and roleOccupant with a DN syntax? ..

9. Displaying results

33. Are the strings used to describe attribute types freely and

independently configurable? [2] ................................

34. Name any attribute types where the attribute values may be

presented in local formats? (For example, it may be possible to

configure the display of telephone numbers so that local numbers

are shown as extensions, rather than with the full international

dialling code.) [1 per attribute, up to a maximum of 4] ........

....................................................................

35. Does the DUA allow for the display of more than one result at a

time (showing attribute values other than the name of the entry)?

If so, how many entries may be displayed in response to a single

query? [2 if feature provided] .................................

....................................................................

36. Does the DUA support the notion of a quick synopsis, where a small

core of attributes is retrieved initially, and a larger set is

returned if required? [2 if yes] ...............................

37. What does the DUA do with attribute types it doesn't support in

its sub-schema, but which have a standard syntax? ..............

38. What does the DUA do with attributes which have are not in its

sub-schema, and which have a non-standard syntax?

(a) Ignore them? ...............................................

(b) Tell user, but don't display? ..............................

(d) Display in some other format? ..............................

10. Association Handling

This section is concerned with how a DUA handles its association with

the Directory.

39. How/where is the access point to the Directory configured? If

more than one method, indicate which ways are possible. [1 per

method, up to maximum of 3]

(a) In a system-wide tailor file ................................

(b) In a per user tailor file ...................................

(d) Other. Please describe .....................................

................................................................

40. Does the DUA allow for automatic connection to a back-up DSA if

the access point DSA is unavailable? [2 if yes] ................

41. Can the DUA keep connections open to more than one DSA at a time?

[1 if yes] ......................................................

....................................................................

42. Does the DUA keep an idle connection open to the DSA(s). If not,

describe the timeout strategy. [1 if yes] ......................

....................................................................

43. Does the DUA handle referrals automatically? [2 if yes] ........

If not: does the DUA handle referrals at all? [1 if yes] ......

44. Does the DUA make use of asynchronous operations?

(a) Does the DUA bind asynchronously? [2 if yes]................

(b) Are the operations handled asynchronously? .................

If so, is this true for:

i. All operations? [2 if yes] .............................

ii. Some operations? [1 if yes] ............................

45. Does the DUA use size and time limits by default? [2 if no

limits, or limits may be over-ridden] If so: ...................

(a) What size limit is used? ...................................

(b) What time limit is used? ...................................

11. Suitability for management

This section is intended to establish the range of operations

supported by the DUA and, in particular, whether it is suitable for

management tasks.

46. Is it possible to invoke all the operations in the Directory

Abstract Service? If not, say which operations it does use [2 if

all] ............................................................

....................................................................

47. Is the user given full control over the service controls? If not,

say which may be controlled, or none at all [2 if full, 1 if some

control] ........................................................

....................................................................

48. Is it possible to manage system attributes with the DUA? If so,

indicate which DSA implementations for which this DUA provides

management capabilities. .......................................

(a) Knowledge [1]................................................

(b) Replication information [1] .................................

49. Access control notwithstanding, does the DUA allow the following?

(a) Attribute management [2 for all below, 1 for some]

i. Addition ................................................

ii. Modification ............................................

iii. Deletion ................................................

(b) Entry management [2 for all below, 1 for some]

i. Addition ................................................

ii. Modification ............................................

iii. Deletion ................................................

iv. Renaming ................................................

12. Query Resolution

This section discusses the process of query resolution. While two

DUAs may both be able to resolve a query using the same information,

one may do so much more quickly than the other. Some DUAs may be

more "economic" in their use of DAP operations to achieve the same

results. Some DUAs may find the correct results even when the users'

input corresponds rather weakly to Directory names. Three aspects of

query resolution are measured:

o Does the DUA actually find the required entry?

o If the required entry is found, how many entries were returned as

well?

o How "expensive" was the query in terms of underlying X.500

operations, whether the query was resolved successfully or not?

The following set of queries might all conceivably be resolved such

that the author's Directory entry be found. The queries are split

into 2 groups: the first group SHOULD pose no difficulties for a

reasonable DUA; the second group are more problematic. In each case,

award [2] marks if the query found the author's entry successfully.

The expensiveness of each query should be measured using the

following formula, which introduces the notion of SearchStones! The

SearchStone rating is calculated by adding together the total

operations used in attempting to resolve a query, weighted thus:

o Bind [5]

o Read operation [1]

o List operation [2]

o Search single level for countries, organisations or

localities [3]

o Search single level for organisational units, people or roles [3]

o Search suBTree [5]

Note: The single level searches have been separated into two

categories in acknowledgement that certain types of search are

much more likely to span multiple DSAs than others. The

weightings are the same for the moment because of the

pervasiveness of the Quipu implementation, which replicates all

sibling entries in a single DSA, whatever the level in the DIT.

The notion of SearchStones merits some further explanation and the

statement of some caveats.

The idea is to give some broad brush view of the work being

undertaken by a DUA to retrieve an entry. There will be some

correspondence between a low SearchStone rating and a DUA responding

quickly, and vice-versa, although this correlation is not consistent,

for reasons given below. It would be desirable to be able to have

some timing information for the resolution of queries, but such

results would only be meaningful if the tests were for target entries

widely distributed throughout the DIT. Maybe this is something for

the future? In the meantime it is worth noting some of the factors

which militate against simple minded interpretation of the

SearchStones.

o The DIT is not uniform, with the depth varying considerably

o While the DIT is currently mastered mostly by DSAs of a single

implementation, this will be decreasingly the case, and other DSAs

may have very different performance profiles.

o Different directory domains are already adopting different

strategies on information replication with profound performance

implications.

o No weighting is given to different search filters, or to boolean

combinations of filters.

While acknowledging the difficulty of the exercise, there are counter

arguments:

o Some DUAs are better than others at finding the required results

o Some DUAs will get the required results more quickly than most

o DUA designers have to build DUAs in the knowledge that the DIT is

heterogeneous with respect to DSA implementation and DIT structure

One possible way forward would be to refine the test queries such

that they better represented the diversity of the DIT. However, as a

first step, the tests are restricted to queries which could

reasonably be constructed as searches for the author's entry. The

author's entry is held in part of the DIT which is representative of

much of the current DIT. It is suggested that in order to normalise

the tests as much as possible, that testing be performed by

connecting to the target DSA directly. The DSA's name is "cn=Vicuna,

c=GB", and the addresses of the DSA may be found in the presentation

address attribute for that entry. Note that the SearchStone rating

should be shown even for queries which cannot be resolved.

First, the straightforward queries:

50. NAME=Paul Barker, OU=Computer Science, O=University College

London, C=GB

51. NAME=Paul Barker, OU=Computer Science, O=UCL, C=GB

52. NAME=Barker, OU=Computer, O=UCL, C=GB

53. NAME=Barker, O=UCL, C=GB

54. NAME=p barker, O=university college, C=GB

55. NAME=paul b, OU=cs, O=university college, C=GB

More difficult queries:

56. NAME=p b, O=university college, C=uk

57. NAME=Paul Barker, OU=Computer Networking, O=london college, C=GB

58. NAME=Paul Baker (sic), OU=cs, O=ucl, C=Britain

59. NAME=p baker (sic), O=UCL, C=England

60. NAME=Paul Barker, OU=Directories, O=london, C=United Kingdom