- 30 CHAPTER 4
DETAILED ANALYSIS OF THE PROBLEMS ENCOUNTERED
Universal Decimal Classification
The flexibility of U . D . C . , provided (a) by multiple possibilities of
placing, according to context, and (b) by the facility for synthesis of
its various auxiliary devices with main numbers, appears to be at once
its strength and its weakness.

Its strength lies in the provision for

exhaustive specification by elaborate synthesis, its weakness in that
if synthesis is carried to extremes by the use of every auxiliary device
which can be brought to bear for a particular document, there is atendency to produce a catalogue with so many 'distributed relatives'that searching is laborious, and indeed, without the use of a very
exhaustive and elaborate index, there is the danger of failure to findeverything relevant to a particular subject.

For example, if thesubject 'damage to gears' in many possible applications is classified
at the numbers for those applications, the following kinds of numbers
are produced :621. 438-257. 004. 65

Damage to gears in gas turbines

621. 313. 12-257. 004. 65

Damage to gears in generators

621. 65-257. 004. 65

Damage to gears in pumps

The searcher must therefore consult each of these numbers and possibly
many others, if his requirement is for 'damage"to g e a r s ' in all its
applications.
One alternative is to colon the numbers for the subject to those forthe various applications, e . g .
621.438: 62-257 : 6.004.65

- 31 in order to provide for permutation for the purpose of bringing all
entries for each aspect of the complex subject together.

Each number

is then used as entry number and reference to a single point in the
catalogue is all that is required to exhaust all possibilities in relation
to a given search.

Another is to combine the two methods by using thefully synthesised number basically, but providing separate numbers forthe various auxiliary aspects for the purpose of grouping.
The latter course would obviously provide a catalogue which would
be something of a hybrid, and it was felt that this would be unsatisfactory.
The first alternative was at first considered to be the best principle,
but it was found that the length of the numbers when coloned together
was unacceptable, that, in practice, the need for elaborate synthesis
was r a r e , and that most subjects, in spite of the complexity of thesubject field, did not lend themselves to the use of many of theauxiliaries provided by U . D . C .
It was decided, therefore, to synthesise numbers by the use ofcommon subdivisions, special analyticals, etc. to whatever degree
was found to be necessary to specify a particular subject as fully as
possible.

The alphabetical index was constructed with a view toovercoming the dangers of losing concepts because of their being
widely distributed under various main numbers. (The compilation of
the alphabetical index is dealt with later in this section).
One specific exception to the general principle of full synthesis
was made.

This applied to the use of 621-4 the numbers for materials

shapes, which it was decided to use always as main numbers.

The

reason for this was that the concepts represented by these numbers arevery often of greater importance than those concepts represented by the- 32 -

main numbers to which they a r e attached.

The latter are usuallymaterials, and the course was adopted of coloning the 621-4 number
to the number for the material and making entries under both coloned
numbers, e.g.
669.715: 621-415

Aluminium alloy sheets

was entered under this form and also under
621-415: 669.715
Additionally entry might also be made under 621-415 coloned directly
to a third number.

This might occur if the subject were f s t r e s s analysisof aluminium alloy s h e e t s ' . when it might be considered that the material
was irrelevant, and entry would be made under :621-415: 531.22
In certain other cases the principle of full synthesis was obviously
not the best course and no rule was necessary to prevent its use.

The

use of the common subdivisions at 629. 13, for parts of aeroplanes, byattaching them to main numbers for particular types of aircraft would
have produced a state of chaos in the catalogue.

This procedure would

have produced numbers such as :629.138.5.014.3

Wings for transport aircraft

629. 138. 5. 066

Electrical systems for transport aircraft

Consequently, a block of such numbers would have appeared under every
type of aircraft encountered in the literature, with the separation ofmaterial on, say, 'air systems' under many different main numbers.
The type of aircraft is usually irrelevant in such c a s e s , and wastherefore ignored, the subject being placed directly at 629.13 with common

- 33 -

s ubdivis ions, e.g.
629. 13.066

Aircraft electrical systems

Where appropriate, use was made of subdivision alphabeticallyby proper names. This was done at such numbers as :629.13(42)(De Havilland - Comet)(Aircraft names, except
helicopters)

629. 135. 45(42)(Westland - Whirlwind)(Helicopter names)

533.6.071(N.P.L. -)(Specific wind tunnels)

621. 432(Bristol - Pegasus)(Piston engine names)

621. 438(Bristol - Orpheus)(Gas turbine engine names)

629.136. 3(Atlas)(Missile names)

669.14(En -)(Specified steels)

When using this device, the basic number was always used, in order tohave a simple sequence of all aircraft, all wind tunnels, etc. It was
felt to be unwise to assign the most specific number possible before
adding the name of the aircraft, material, etc. , as in :629. 138. 5(42)(De Havilland - Comet)
In these c a s e s , the type of aircraft (transport), etc. is specified before
adding the designation, but when information is required on such topics,
it is usually sought by the names used, and a single sequence of allaircraft, all wind tunnels, etc. , is the preferable method. Where it
was thought to be justified, entry was also made under the full number,without the addition of the alphabetical designation. This sort ofrequirement arose when material on a designated aircraft might havebeen of interest both from the point of view of that aircraft, and fromthat of the type of aircraft, e.g. entries for the subject 'ground equipment

- 34 -

for the Comet* might reasonably have been made under :629. 13(42)(De Kavilland - Comet): 629.139 (Ground equipment
for Comet)
629. 138. 5: 629.139(Ground equipment for transport
aircraft)

Certain decisions had to be made with regard to the use of particularnumbers for particular purposes, where ambiguity existed in theschedules.

A particular case of this kind is the treatment of s t r e s s e s ,deformation, and strength in 53. The following rules were followed
for this purpose :1. The various kinds of s t r e s s e s are to be placed at 531. 22mand its subdivisions, e.g. Bending s t r e s s e s 531.224
2. The deformations resulting from these s t r e s s e s are to beplaced at 539.38 and its subdivisions, e . g . Bending 539.384
3.

The ability to resist these s t r e s s e s , i . e . strength, is to beplaced at 539.4 and its subdivisions, e.g. Bending strength539 413.

A rule had also to be made for the application of the numbers
533.692 and 533.693. The former is provided for material on section
shapes, the latter for wings in general.

Confusion a r i s e s , however,when subjects such as 'cambered wings', ! sweptback aerofoils 1 , etc.
appear.

The following rule was made to clarify this problem :533.692 is to be used for ail two-dimensional aerofoils,
including wings, and for three-dimensional aerofoils andwings when the shape of the aerofoil section is paramount.
For three-dimensional aerofoils and wings in general,
particularly when planform is paramount, 533.693 or its
appropriate subdivision is to be used.

One of the greatest difficulties in applying U . D . C . is the achievement of consistency in the way the various available numbers andauxiliary devices a r e used.

The kind of problem which a r i s e s i s the

specification of m a t e r i a l s in various applications.

F o r the subject'raw m a t e r i a l s for turbine blades for gas turbine engines 1 the number
621.438.1-253.5.002.3 may be used. If the subject is 'steel forturbine blades for gas turbine engines 1 , then the number should be
6 2 1 . 4 3 8 . 1 - 2 5 3 . 5 . 0 0 2 . 3 : 669.14. In practice one seldom s e e s the useof the . 002. 3 number, because it is apparently redundant in that thesteel must obviously be the m a t e r i a l of which the blades a r e made.
It is also very difficult to r e m e m b e r all the applications in which the'points of view' numbers and other auxiliaries should be used, butthey ought to be used always— because of thep separation of related
subjects by their absence :1.

621.438.1-253.5.002.3

Raw m a t e r i a l s for turbine blades2.

621. 438.1-253. 5; 621. 9 % Machining of turbine blades3.

621.438. 1-253.5: 669.14

Steels for turbine blades

1 and 3 ought obviously to file together, but are separated because of
the absence of .002.3 in 3. An exactly analogous problem a r i s e s inalphabetical subject cataloguing, because of the tendency to ignore theobvious and the avoidance of the inclusion of redundant t e r m s .

Theya r e redundant as far as the statement of the subject is concerned, but
certainly not from the point of view of filing o r d e r :1.

WINGS - Sweepback

2.

WINGS, CRESCENT

3.

WINGS, DELTA

4.

WINGS, SWEPTBACK

- 36 -

This separates material on sweptback wings, and the solution to the
problem would be to include all qualifying t e r m s in every case.

The

difficulty of ensuring such consistency and the resulting comple
with undesirable headings such as :WINGS, SWEPTBACK - Sweepback
GASES, COMBUSTIBLE -Combustionand class numbers of a similar structure in U . D . C . militate against
the workability of such a procedure and it was felt that the adoptionof the principle was not justified.
The many cases in which several different numbers are available
for placing a given concept repeatedly caused difficulty.

This problem

1

seems to stem basically from the ' t r e e of knowledge basis of U . D . C .
which has resulted in the development independently of specific a r e a sof the scheme.

The inevitable result is that each of several differenta r e a s draws in a common subject as reasonably belonging to that a r e a .
The subject 'lubricants' for instance appears at 62-72, 62i.89 andcould conceivably appear in 665, Whilst the context often shows theappropriate place for a given document, it is difficult to make adecision between numbers such as 62-72 and 621. 89. The problem iseven more complex when a subject such as 'Fuel systems for ram jets
for test vehicles' is encountered.

'Ram jet propelled test vehicles'

should be placed at 629. 138.744.035.53. A number for fuel systems
exists at 629. 13.012. 525.3, but there is also the number 621.439.4.032
for 'fuel systems for r a m jet engines'. F o r the sake of grouping in themost convenient way, the tendency was to use whatever appropriate main
numbers were available, with one or more auxiliaries, and colon where- 37 -

appropriate.

This subject was therefore placed at :-621.439.4.032: 629.138.744.035.53
and a second entry made by reversing round the colon. The firstnumber in each case has some real significance in its own right, andthough the whole entry is rather long, and the concept 'ram jet engines 1
is repeated, the second number does qualify the first.

It is on problems

such as this that the Facet scheme appears likely to score.

The 'oneplace' principle inherent in Facet should go a long way to helping inthis respect.
The various kinds of provision made for auxiliaries also show
serious inconsistencies in the scheme, and though good alphabeticalindexing will to a large extent, rectify these faults, there seems to be
no reason why some rationalisation of the scheme should not eliminate
many of them.

A simple example of this is the provision at 621.43. 018. 55

for 'starting' internal combustion engines.

There is also provision at

the more basic number 621-57 for 'starting' and it is unfortunate that
this duplication has been allowed to creep in. The number used for'starting afterburners' was in fact 621.438.019.93.018.55, but it could
have been 621.438.019.93-57.

The reason for this was that wherecommon subdivisions, etc. existed at the particular level of the schedules
in question, (in this case 621.43), then those subdivisions were used in
preference to those at the more basic number (in this case 621-).
At the same time, the analysis of a complex subject so logically as
to ensure a 'one place' arrangement completely free from overlapping
and ambiguity is extremely difficult.

Facet analysis seems to be theproper approach to the problem, but in the present state of the art it is- 38 -

doubtful whether even this approach has reached a sufficiently
sophisticated level to justify claims that it will be an improvement
on a system based on the ' t r e e of knowledge 1 principle, with itsschedules largely empirically derived. It is this sort of question
which it is hoped the testing will answer.
Where no place could be found for a specific subject, the usual
procedure of using the number for the containing head was followed,
if it was felt that a new number could not satisfactorily be assigned.
This is a most unsatisfactory answer to the problem, for a subject
such as 'stagnation point1 had to be placed at 532. 526 (boundary layer).
It was often necessary to link this subject with a subject which was a
subdivision of the number so assigned (in this case perhaps 'laminarboundary layer'). It is patently unsatisfactory to have such entries
as 532. 526. 2: 532. 526. F o r this reason the procedure was avoided
whenever possible, and a new number created for the subject.

The

argument that the principle is acceptable, provided that the subject
is entered in the alphabetical index to the classified catalogue, canhardly be accepted h e r e .
Alphabetical index to U . D . C
One very striking feature regarding the use of classified catalogues
is the difference in emphasis placed on the value of an alphabetical index
of high quality, as between the users of Dewey in public l i b r a r i e s , andthe u s e r s of U . D . C . in special l i b r a r i e s .

The very low standard ofalphabetical indexing in special libraries probably stems from a
confusion between 'indexing* and 'cataloguing'.

If'cataloguing 1 istaken to mean 'listing' (and this is a dictionary definition, not aninvention of documentalists or bibliographers), then it follows that an

- 39 -

index is needed to 'point out1 (again a dictionary definition) the
location in the catalogue of a given subject, unless the catalogue happens
to be of the kind where the known order is an alphabetical order of thenames of subjects (an 'alphabetical subject catalogue 1 ).

Unfortunately

1•indexing has been used loosely to describe the listing, or cataloguing,of subjects in classified order ( e . g . U . D . C . order) and the alphabeticalindex to this list has been regarded as of little importance.
The development of faceted classification systems has again put
the alphabetical index into proper perspective, because it is rightly
recognised that the index is an integral part of such a scheme of
information retrieval.

Moreover the principle of 'chain indexing' has

introduced a rigorous discipline into the compilation of such indexes.
It was felt that the misconception outlined above should be squarely
faced for the purpose of the project and that, as with all other threesystems, no shortcomings which could reasonably be eliminated shouldbe allowed to jeopardise the fair comparison of U . D . C . with the othersystems.

It was decided at the outset, therefore, that the best possiblealphabetical index should be compiled in the course of indexing.

There

is apparently little literature on this aspect of the classified catalogue(Footnote 1) and the actual form of headings, etc.had to be decided in thelight of experience.

Footnote

It is not sufficient to lay down that each term in theThis is just one of a number of statements in this chapter

which was (to the best of our knowledge), true at the time of writing thedraft of this report, and equally true in 1958 when work on the projectcommenced.

The position has changed with the publication of the book

"Subject catalogues, headings and structure" by E. J.Coates, (London.
The Library Association. 1960).

40 -schedules which is used must be indexed, for problems of the formof heading for each entry are just as pronounced as those encounteredin alphabetical subject headings work.

The basic principle on whichindex entries were formed was that of selecting the word or words
representing the most specific elements of the class number indexed,
and adding the t e r m s for superordinate classes in ascending order, tothat level which it was considered would eliminate ambiguity bydifferentiating between homonyms and between entries for the same
subject in different contexts. No attempt was made at chain indexing,i . e . the superordinate t e r m s were not indexed as a matter of course,
though many of them appeared as index entries in their own right,
because documents appeared on the subjects which they represented.
The type of entry produced by this method was as follows :Cooling. Gas turbines. Internal combustion engines.

621.438-71

Performance. Gas turbines. Internal combustion
engines.

621.438.018. 5

Blades, Turbine. Gas turbines. Internal Combustion
engines.

821.438.1-253.5

Flip-flops. Electronic switches. Relays. Electricalengineering.

621. 318. 572

This produced a standard form of entry and worked very well, but
it was felt that whilst entries of this type should all be included, amodified type should be made additionally in some c a s e s .

The entry

term 'performance' for instance, is unlikely to be sought except inconnection with the 'thing 1 whose performance is concerned.

The t e r m'production' could conceivably be useful for the s e a r c h e r interested in
production methods generally, and not just in connection with gas
turbines, whilst 'blades; turbine' certainly ought to be used as entry t e r m .

- 41 For these reasons, in many cases an additional entry was madeby transposing the entry term to the end of the heading, producing
entries of the form :Gas turbines. Internal combustion engines. Cooling.
"

"

"

"

"

. Performance.

The transposed term was underlined to show that this had been done.
In the vast majority of cases the terms transposed were of thekind which in a faceted classification would fall into the 'energy 1 facet,i . e . operations, etc.

There were a few exceptions to this rule such as

properties (e. g. 'vulnerability') or substantives (e. g. 'materials'), butparts, such as 'blades, turbine' were never transposed.
The reason for transposition were as follows: if the form of entry
produced by the basic rule is the only type used, then in some cases
the substantive part of the entry ( e . g . 'gas turbines') would not appear
as entry word, and this is obviously undesirable.
made for this by part or whole chain indexing.

Provision could be

The argument put

forward for chain indexing is that if a higher term than the most
specific is selected for entry into the classified catalogue, the subdivision of this term is self evident by the arrangement in the catalogue.
But it is also admitted that the arrangement has to be supplemented bysuitable guiding in the catalogue and this surely can only be described
as 'listing' the subdivisions, for if the arrangement were in a known
and recognisable order, guiding would be superfluous.

The method offinding a specific topic by searching for it under the containing head(say 'Gas turbines') in perhaps three drawers of catalogue cards canhardly be claimed to be logical.

This does, in fact, amount to 'sorting

through' as distinct from 'known order'.

It was felt, therefore, that as

- 42 -

the known order (alphabetical) was the basis of the index to U . D . C . ,its extension to showing the particular points in the catalogue at which
subdivisions of a subject would be found would serve a useful purpose.
The result was groups of entries of this kind :Gas turbines. Internal combustion engines.
If

ft

n

"

* Breathing.

IT

II

u

"

. Combustion.

It

II

ti

Control.

ri

it

n

Cooling.

if

ti

it

Damage.

e t c . , etc.

In a few cases two t e r m s were transposed, particularly where
one was an operation ( e . g . 'measurement') on another ( e . g . 'property'):
Noise. Acoustics. Physics. Intensity. Measurement.
In a few others, where a superordinate t e r m was likely to beunsought (though useful as a qualifier in the basic entry), both entry
word and superordinate t e r m were transposed, but the basic entry word
was placed before the superordinate t e r m , e . g .
Wind tunnels. Density. Tunnel conditions.
. Humidity.
Though chain indexing was not practiced, some of the principles
relative thereto are obviously relevant h e r e .

One of these is

Ranganathan's statement that the breakdown in the classification should
show an 'expressive structure' , i . e . it must be hierarchical.

It isevident that the breakdown must not only be expressive, but must be
consistent in its expressiveness, if searching is to be a logical process.

- 43 -

In other words, if in one part of the schedules p r o c e s s e s ' are to follow'concretes 1 , then this must be the arrangement in all other parts ofthe schedules. It is inherent in a faceted classification that this consistency is achieved, but it is certainly not always the case in enumerative schemes and U . D . C . is a case in point. If the alphabeticalindex to the classified catalogue is to be based on the principles adopted
for use with U . D . C . on the project, then such inconsistencies must
inevitably be reflected in the index.
Perhaps the worst example which we encountered of this inconsistency in U . D . C . is the treatment of the process 'measurement 1 .
Provision is made at 534. 839 for 'measurement of noise', at 534.61
for 'measurement of intensity of noise'.

Both of these are main

numbers, without the necessity for synthesis by common subdivision,etc.

At 53. 08 provision of common subdivisions is made, and it was

found necessary to use these, for instance, at 536.2.08 for 'measurement of conductivity'.

At 531. 7 is a substantive number for 'measure-ment of geometrical and mechanical magnitudes', divided by the kindsof thing measured, such as 'density' at 531.75, 'height' at 531.719.4,
etc. , this being the reverse of the 'thing - process' breakdown at such
numbers as 534. 839.
It is impossible to cater for all difficulties of this kind, and theentries under 'measurement' for those numbers under 531.7 wereomitted. Entry does appear, however, under the thing measured inevery case, regardless of the section of the schedules from which thenumber is derived.
Another difficulty of the same kind arises because of inconsistency
in the method of splitting down a physical 'thing' into its component parts.

- 44 At 6 2 1 - 2 5 3 . 5 provision i s made for 'blades for turbines 1 , this number
not being a subdivision of a number for 'turbines 1 .

At 6 2 9 . 1 3 . 0 3 8 . 1 2provision i s made for ' b l a d e s ' , the number being a subdivision of
6 2 9 . 1 3 . 0 3 8 . 1 for ' p r o p e l l e r s ' .

If the r u l e s for index e n t r i e s w e r erigidly followed h e r e , the following e n t r i e s would result :Turbine b l a d e s . Machine components. Mechanical engineering.^
621-253.5
B l a d e s . P r o p e l l e r s . Aircraft engineering.

629.13.038.12

To avoid this i n c o n s i s t e n c y , in c a s e s of this kind, the adjectival f o r m
w a s r e s o r t e d t o , and entry made under the t e r m s in the inverted anduninverted f o r m s :B l a d e s , Turbine.
Turbine b l a d e s .
Blades, Propeller.
Propeller blades.
C a s e s a l s o a r i s e where the headings are inevitably adjectival inform.

F o r i n s t a n c e , the number 629. 1 3 8 . 5 r e p r e s e n t s 'transport

aircraft'.

In t h e s e c a s e s entry was made under both inverted anduninverted f o r m s :Transport aircraft. Aircraft engineering.

629.138.5

Aircraft, Transport. Aircraft engineering.

629.138.5

Further to t h i s , the number could be qualified by the addition of
the c o m m o n subdivision 0 3 5 . 6 for 'turbine-propeller propulsion'.
This number can r e p r e s e n t either 'turbine-propeller propulsion oftransport aircraft' or ' t u r b i n e - p r o p e l l e r transport a i r c r a f t ' .
A s s u m i n g the latter to be the c a s e , entry would be made under :' T u r b i n e - p r o p e l l e r transport aircraft. Aircraft engineering.'

- 45 Entry would also be made under the two forms quoted above, extended
to include the new qualification :Transport aircraft, Turbine-propeller. Aircraft Engineering.
Aircraft, Transport, Turbine-propeller. Aircraft Engineering.
Entry was therefore always made under the fully inverted forms andno entry was made for :Aircraft, Turbine-propeller passenger.
This arrangement tended to group subjects more satisfactorily,
as the adjective immediately following the substantive, in a fully
inverted heading, was usually of greater importance than the second
adjective.
No attempt was made to index compound numbers formed by theuse of the colon, except for a few concepts which, though being
regarded as an entity, have as yet no provision in the schedules,
except as coloned numbers, e . g . ' c e r m e t s 1 : 666. 3: 669.
Schedules
The British Standards Institution a r e the responsible body inEngland for the publication of the schedules of the U.D.C and thefollowing published schedules were used in the project :BS.1000A U . D . C . Abridged English Edition
BS. 1000 Vol. 1, Pt. 1 Auxiliary tables
Vol.2, P t . l Classes 50, 51, 52, 53
Vol.2, P t . 2 Class 54
Vol.2, Pt. 3 Classes 55, 56, 57, 58, 59
Vol.4, P t . 2 Class 621.3(622/623) Class 622, 623(669) Class 669(678-679) Class 678, 679

- 46 -In addition we used supplementary schedules for the following
sections which were of particular interest to the subject field of the
project :Class 532. 5 and 533.6
Class 6 2 - , 620, 621.1/2
Class 621.7, 621.8, 621.9
Class 629. 1
The schedules for these sections have been worked out in greater
detail than was available in the printed editions, but they have not beeninternationally approved.

The schedules covering 532.5 and 533.6

were a revision of the existing schedules put forward by the Aslib
Aeronautical Group. The schedules for 533.6 Aerodynamics are
reprinted in Appendix B together with a sample page of the alphabeticalindex.
Alphabetical Subject Catalogue
Before the commencement of work, a survey was made of existing
subject headings lists, and information relevant to the compilation ofalphabetical subject catalogues, in an attempt to find (a) a list which
would form a nucleus for the building up of a suitable set of headingsand (b) rules or guiding principles which would ensure consistency inextending the list as the work proceeded.
Certain lists, which were mainly of U.S. origin, were examined
but were all found wanting for our particular purpose.

Possibly themost satisfactory seemed to be the Special L i b r a r i e s Association'List of Subject Headings for Aeronautical Engineering L i b r a r i e s ' , but
it was inadequate on three counts :-- 47 -

a. It did not contain many of the headings requiredb. Those headings which it did provide were too broadc.

There was no facility for building compound headingsof sufficient specificity.

The attempt to find literature on guiding principles was even lesssuccessful.

Most of what has been written seems to be devoted to the

problem of what entries ought to be made to cover adequately the
subjects of documents, i . e . the principles of multiple entry, and thetechnique of 'see 1 and 'see also' referencing.

What was sought for the

purpose of the project was, in effect, a 'grammar 1 of subject headings,
that is the principle of forming consistently individual headings of any
degree of complexity.

The problem of multiple entry under such headings,

and the linking of headings by references, whilst admittedly a complex
problem, was felt to be subordinate to this fundamental problem of whatform an individual heading should take. Indeed, the solving of the firstproblem should contribute to the simplifying of the second.
One of the latest excursions into the field of alphabetical subject
cataloguing was the article by E. J.Coates 'The use of B.N. B. in
dictionary cataloguing' (Ref. 14). This, advocates the derivation ofsubject headings from the schedules of a classification scheme and inprinciple is an excellent system for mechanically marshalling terms,
and ensuring their proper linkage by way of referencing.

This is thekind of principle which workers in the field of information retrieval
would like to see established as it removes cataloguing from the realmsof art and establishes a science, but unfortunately this particular method
appears to suffer from two fatal weaknesses :a. It does not provide for the actual form of individual
headings (the 'grammar' mentioned above)b. It presupposes a perfect classification scheme- 48 -

With regard to (b), not only i s there as yet no such perfects c h e m e , but a given subject i s capable of breakdown by m o r e than
one s y s t e m of c h a r a c t e r i s t i c s .
p r e f e r r e d order1This i s borne out by the fact thatin faceted s c h e m e s i m p l i e s that there i s choiceof o r d e r , and consequently different p o s s i b l e breakdowns.

It i stherefore p o s s i b l e to d e r i v e different kinds of subject headingsl i s t s b e c a u s e of the dependence of linking of headings by referencing
on s e v e r a l different p o s s i b l e c l a s s i f i c a t i o n s c h e m e s .
It was felt that it would be unwise to adopt the principle for the
purpose of the project because it i s p o s s i b l e that the quality of thesubject catalogue would suffer rather than gain, by being lied toclassification.

Though c o n s i s t e n c y i s achieved, the method l i m i t s

flexibility in compiling a subject headings l i s t , and it w a s felt thatit should be left to the i n d e x e r s to make the best p o s s i b l e list byknowledge of relationships gained in the c o u r s e of indexing.

Itwould a l s o have been unwise to c o m p a r e a subject catalogue basedon headings derived from one of the c l a s s i f i c a t i o n s c h e m e s usedon the project, with a c l a s s i f i e d catalogue using that s c h e m e , for
it i s p o s s i b l e that the free choice of t e r m s for subject headings i san advantage compared with the rigid grouping of t e r m s in a
c l a s s i f i c a t i o n s c h e m e , at l e a s t in a s c h e m e of the enumerative typesuch as U . D . C .

It i s p o s s i b l e that the t e s t i n g p r o g r a m m e will throws o m e light on questions such as t h i s .
When indexing began, the S . L . A . list was used a s a b a s i s forthe building up of a subject headings l i s t , but as work proceeded
and the particular r e q u i r e m e n t s of the project b e c a m e c l e a r e r , new- 49 headings were generated quite independently and at this stage an
attempt was made to formulate some simple r u l e s .

These rules

were found to be somewhat restrictive and slight modifications were
therefore made. In their final form the rules were as follows :1. Headings
Headings are composed of Main Headings with Sub-headings
if required.
2. Main Headings
The Main Heading is composed of a noun (or a phrase), ora noun qualified by one or two adjectives.

Normally aninverted form is used, so that the adjective follows thenoun. A comma is interposed between the noun and theadjective, e . g . DIFFUSERS, WIND TUNNEL.

Where

TRANSONIC, SUPERSONIC or HYPERSONIC is used toqualify a heading in addition to another adjective, thisspeed qualification is to be regarded as subordinate and is
to be placed last, e . g . DIFFUSERS, WIND TUNNEL,
SUPERSONIC. Where common usage demands, the uninverted form is used, e.g. WIND TUNNELS. In caseof ambiguity, where the same word can be used withdifferent meanings,

a defining t e r m may be added insquare brackets, e.g. BLOWING [ BOUNDARY LAYERCONTROL ] . Names of specific items may be added incurved brackets, e . g . AEROPLANES (DE HAVILLAND COMET), AEROFOIL SECTIONS (NACA 64010), ASPECTRATIO (9.43).

- 50 3. Sub-Headings
Sub-headings are used to qualify the main headings and a r e
preceded by a hyphen. In general, sub-headings fall into
three groups :a-

P r o c e s s e s such as "Production" or "Anodising"b.

Things which can be measured, calculated orotherwise determined
F o r example 'lift' can be measured. 'Stress
distribution 1 can be calculated, 'collapse' canbe determined.

c.

Form such as "Charts"

In some c a s e s , sub-sub-headings may be used further toqualify main headings and sub-headings, e.g. WINGS Lift. Measurement.
These rules may appear to be inadequate for the purpose ofbuilding up a subject headings list in a field as complex as aeronautics,
but it appeared that there were two alternatives: either to use a
simple set of rules of this kind and decide on individual headings as
they a r o s e , or to endeavour to cover every individual case whichmight a r i s e .

There is little doubt that the complexity of the second

alternative is the reason why no satisfactory guiding principles exist,
and m fact the end result would doubtless consist not of a set of rules,
but of a list of a r b i t r a r y decisions, one for each heading used.

This

result is reached in practice, of course, in that the subject headings
list itself is a list of t e r m s resulting from such a r b i t r a r y decisions.
Inevitably, there is inconsistency in the form of headings used becauseof the impossibility of determining form in principle, instead of by

- 51 empirical decisions on individual headings.
The provision of rules to meet every case would determine
unambiguously what the form of a heading should be for both indexer
and s e a r c h e r , and this would ensure that coincidence between the two
which is the essence of successful information retrieval.

To

illustrate the magnitude of the problem, the following is a list ofsome of the possible adjectival qualifications of 'blades 1 :Blades, Steel, Twisted, Hollow, Propeller, Thin, Supersonic, Tapered, Adjustable
It is conceivable that it may be necessary to form a heading of thiskind :Blades, Propeller, Steel, Twisted, Tapered, Hollow, Supersonic.
It is difficult to imagine what logical analysis of a subject could possibly
determine in what order these qualifications should be. In practice,of course, it is possible to determine the sequence by using facet analyses
and having categories of t e r m s , with the categories arranged in a•preferred* order.

But this is a specification of only one kind of object(a 'blade') and the order that is suitable for this will not necessarily be
the best for other subjects.

The question of 'preferred order' and theunlikelihood of a single commonly acceptable order has already been

- 52 -

mentioned and will be discussed again in the section on the Faceted
Classification Scheme. Additionally, the characteristics which
determine these qualifications, may as a group be quite different fromthose required to analyse another subject, and each case seems to need
its own rule.
This aspect of the problem is only the beginning of the difficulties
encountered in subject headings work.

Simple adjectival qualificationsof this kind, whilst presenting difficulties in the alphabetical subject
catalogue, cause no complication emanating from 'relational' problems,
because they merely exist side by side as characteristics which theobject p o s s e s s e s , and it is likely that mechanical sorting could
satisfactorily handle them without the risk of 'false drops'.

There isusually, however, the need further to qualify a heading by sub-headings
to show wuch things as p r o c e s s e s , the conditions under which processes
are applied, the 'agents' in the p r o c e s s e s , properties, problems,applications, etc.
It is at this stage that the forming of headings becomes reallydifficult.

Certain kinds of relations between subjects a r e recognisable

in practice, but it is impossible to estimate how many such relations
may exist in the field of human knowledge.
relations encountered in indexing were :a.

Affected by -b.

Affecting -c. Compared with d. Applied to e. Controlled by f.

Controlling -g. Under the conditions of -Some such recognisable- 53 Examples of the contexts in which these relations might be relevant
are as follows :a.

Boundary layer transition - affected by - surface roughnessb.

Boundary layer transition - affecting - dragc.
d.

Aluminium - compared with - steel (for a particularapplication)
Computers - applied to - air traffic controle.

Missiles - controlled by - gyroscopesf.

Tapes, Magnetic - controlling - machine toolsg.

P r o p e l l e r s - under the conditions of - supersonic speed(This is a different concept from that of propellers
designed for operation at supersonic speed, i . e .
P r o p e l l e r s , Supersonic)

This type of problem is a far cry from the simple principles
advocated by those such as Kaiser (Ref. 15). His f concrete' and' p r o c e s s ' methods make for consistency and are excellent for thetype of catalogue which does not demand the specificity required insuch a field as that covered by the project.

It is obvious that the examples

given above are not the only forms in which the subjects might be stated,
and that some ( e . g . a. and b.) are complementary in that the twodirectional relations 'affected by' and 'affecting' can be reduced to asingle one-way relation by transposition of the t e r m s .
It was evident that the magnitude of the problem of rationalising thetypes of entry was such that any attempt of this kind was out of thequestion.

The chances of success were, in any c a s e , slim in the present

state of the a r t .

It was felt, therefore, that it was unwise to go further

than the use of the type of heading permitted by the rules set out above,- 54 i . e . a main heading consisting of a substantive and a maximum of two
adjectives, together with a maximum of two subheadings.

Usage

usually decided the order of two adjectival qualifications and in thecase of speed ( e . g . 'supersonic'), this always appeared as the lastword in the main heading, e . g .
WINGS, SWE^TBACK, SUPERSONIC
As far as sub-headings were concerned, where two were used,
it was usually clear what the order should be, as the second qualified
the first, e. g.
WINGS, SWEPTBACK, SUPERSONIC - Lift. Measurement.
An early decision which had to be made was whether to use theprinciple of direct entry or inverted headings. It was decided that theinverted form should be used, firstly on account of the useful grouping
which this brings about, and secondly because of the advantage ofeliminating what would have been extremely elaborate referencing.

Itseems that most of the writings on alphabetical subject headings work
has been concerned with the cataloguing of very general material,
where subjects fall into a very large number of largely separate pigeon
holes, with only comparatively small groups of such subjects needing
linking by c r o s s reference.

In a field as complex as aeronautics, thepattern is such that direct entry would lead to the separation of large
numbers of headings which are usefully grouped by inversion.
It is not practicable to state categorically that all headings must
be inverted, because the relative significance of substantive andqualifier varies very considerably from one t e r m to another.
following examples illustrate this :-The- 55 -a.

Double flapsb.

Fuel i n j e c t o r sc.

Generating plant

It i s evident that to enter (a) in the univerted form i s to place the entry
where it i s v e r y likely to be unsought,(b) i s a doubtful c a s e , where

it might be argued that either form would be a c c e p t a b l e , whilst (c)i s a c a s e where what i s s t r i c t l y the substantive part of the heading(plant) is such a nebulous t e r m that entry under it would invite riskof l o s i n g the m a t e r i a l indexed.

T h e s e e x a m p l e s show the two e x t r e m e s ,and a middle c a s e where the balance in favour of one word or the otheri s not d e c i s i v e .

In practice e v e r y d e g r e e of difference in e m p h a s i s

i s met and d e c i s i o n s can only be made on the m e r i t s of the particularc a s e , and not by rule.

Exception to the basic requirement that headings

should be inverted was t h e r e f o r e made where usage definitely demanded
the uninverted form and where the substantive was decidedly of l e s ssignificance than the first t e r m .
One feature of the r u l e s about which s o m e doubt was felt was thatthe facility for using a substantive as a subheading was excluded/This was c o n s i d e r e d to be a disadvantage in s o m e c a s e s , a s s o m e
useful headings could have been made in this manner.

A particular

example i s the d e s i r a b i l i t y of being able to use 'boundary layer 1 a s
a subheading,e.g.

CONES - Boundary l a y e r
The n o n - e x i s t e n c e of this rule would a l s o have enabled n a m e s of partsof things to be used a s subheadings,

e.g.

ENGINES, RAMJET - Fuel s y s t e m s

- 56 -

This, of course, is tending towards alphabetico-classed entry, andit was certainly not intended that this principle should be used.
this reason, the rule was probably justified.

For

It was satisfactory inthis case to use :FUEL SYSTEMS, RAMJET
which is no less specific than the thing-part type of entry, andwhich is manageable with proper 'see also' referencing.

This formof heading could not be used to solve the e a r l i e r problem, as it
would have produced :BOUNDARY LAYER, CONE
This again illustrates the existence of many different shades of meaningand different relationships which make the consistent forming ofheadings so difficult.
It is doubtful whether the qualifying t e r m s 'ramjet' and 'cone'in the inverted headings quoted could legitimately be called 'adjectival',
but whatever they may be, further problems a r e created when twq suchqualifiers appear.

'FLYING BOATS, SUPERSONIC and 'BOATS,FLYING, SUPERSONIC1 are both acceptable, but 'AEROFOIL THEORY,
SUPERSONIC is not strictly correct as the only t e r m to which 'supersoniccan apply is 'aerofoil'.

'Aerofoil theory' as an entity cannot be supersonic

The form given above was in fact accepted as being in general use,though AEROFOILS, SUPERSONIC - Theory might be better.

However.

the undesirable headings which can be produced by using the latter method
to break down everything of this kind a r e illustrated by the examples
given by Prevost in her article on theory and method in general subject
headings (Ref. 16).

- 57 -

Alphabetical subject catalogues seem to be at their weakest whenconcerned with two or more substantives linked by one or more relationships.

The subject 'the diffusion of light rays in turbulent boundary
1layers can be catered for only partially satisfactorily, and would
probably take the entries :BOUNDARY LAYER, TURBULENT - Properties
LIGHT - Diffusion
No doubt the subject would not be lost, but in a large collection of
documents in a specialised field, this kind of problem becomes acute,and greater specificity is required.

The form of entry quoted above,

was in fact the kind used during the indexing, but the indexers wereconscious of the fact that greater sophistication will be required in
the future as quantity of documents and complexity of subject increase.
The facility for incorporating names of specific aircraft, engines,
aerofoil sections, etc. was provided and was used as with the othersystems.

The facility for showing quantitative values of aspect ratio,

sweepback, etc. was also provided, but the tendency was not to use
this much, as the headings could not normally be as specific as wasdesirable in the first place and the use of bracketed quantities was not
likely to relieve the situation.
In spite of apparently insoluble problems on this question of specificity,
the alphabetical system may prove to be far more satisfactory than would
appear, for the reason that the specificity provided by other systems
may be a snare and a delusion. The testing will show up the respective
merits of the various systems.

- 58 -The question of c r o s s - r e f e r e n c e s was another matter on which
we were unable to obtain much practical guidance. Normal " s e e "references were of course, made in all cases of inverted headings andsynonyms, and it was also a routine procedure to index "see also"
references where a t e r m for a main heading was also used as a subheading, e.g.
ANODISING, see also as sub-heading with specificsubjects, e . g . BRASS - Anodising
Our problem came with "see also" references which linked
related subjects, and after long discussion it was decided that theseshould, for the purpose of the indexing, not be used.

Our reasonsfor this somewhat radical departure from accepted practice are
given below.
Firstly it is necessary to consider the reason for including"see also" references.

A subsidiary use is to suggest to the indexers

other or more suitable headings. Their main use 5 however, is in the
retrieval of information, the intention being that where the s e a r c h e r
fails to find all the information he requires under a particular heading,
he will find references to other subject headings which may possibly
contain relevant information.
"See also" references can be of various kinds. They can referfrom the general to the more specific, e.g. Aircraft see also
Airplanes. Airships, Balloons, Cyclogyros; Gliders; Helicopters;
Rotor Aircraft, or from the specific to the general, e.g. Airplanes
see also Aircraft.

Alternatively they can refer to subjects relatedon the same level, e.g. Seaplanes see also Flying boats, or they can

- 59 refer to subjects which basically appear to come into a separate
category, e . g . Machinery see also Patents.
It i s , presumably, a policy decision as to which of these types of"see also" references should be used, and in the S.L. A. "Subject
headings for aeronautical l i b r a r i e s " , there appears to have been thedecision not to refer from the specific to the general in the case ofphysical objects, so we do not find the example given above "Airplanes
see also Aircraft".

With theoretical subjects, however, this rulingdoes not appear to apply since we find "Flow of Fluids see also
Fluid Mechanics; Fluids; Hydraulics;".

The other examples

given in the preceding paragraph are taken from the S. L. A. list, andwe attempted to find the basic principles which governed the compilationof the "see also" references.
We immediately became aware of a number of contradictions which
are illustrated by the examples given above.

"Aircraft" can reasonably

have "see also" references to "Airplanes; Airships; Balloons; Rotor
Aircraft", but "Cyclogyros; Helicopters" are types of "Rotor Aircraft"from which they receive "see also" references, together with
"Autogyros".

"Airplanes" has "see also" references to "Amphibians,

Biplanes, Flying Boats, Hydroplanes, Seaplanes," and there appears noreason why these should not also be listed under the "see also" referencesfrom "Aircraft" if "Cyclogyros; Helicopters" are to be so included.
If related subjects at the same level, such as "Seaplanes see also
Flying Boats" are to be given, then one would have expected to find"Cyclogyros see also Autogyros", but there is no such entry.

The

person searching under "Ailerons" will find no "see also" references- 60 unless he thinks of the containing head "Control Surfaces".

Under"Flaps" he will find "see also Air brakes" but if he should go straightto "Flaps, Dive", he will find no such cross reference.
The inconsistencies in the S.L. A. list are not peculiar to thisparticular list, but were apparent in a number of other lists which we
reviewed, and we mention this list only because of the authority which
is given to it by the number of distinguished persons who helped inits compilation. We came to the conclusion that "see also" referenceswere made in a haphazard and arbitrary fashion, a fact which wasborne out in correspondence with a number of librarians in Canada andthe United States.
To do the job thoroughly, it would seem that every time a newheading was generated it would be necessary to go through th e complete
list of headings to ascertain which of the headings merited "see also"
references.

If this were done conscientiously it would take care of all

the required "see also" references from the general to the specificand also the references to allied subjects at the same level, but itwould obviously be a very time-consuming task.

The only logical methodof doing this work appeared to be by compiling a set of classified
schedules or alternatively a form of thesaurus which would embrace all
the headings in the list and which could be used by searchers wheneverthey wished to have ideas of new headings to search. It is not a newproposal that "see also" references should be constructed in this manner,
but we were unable to find any cases of its having been done in any subject
field approximating to aeronautics.

If such a schedule or thesaurus iscompiled and used, it must obviously carry the implication that there is
no guarantee that useful information will be found in any of the other- 61 headings. We look the view, as strongly stated by Metcalfe (Ref. 6),that there is no justification to use c r o s s - r e f e r e n c e s in an attempt tojustify bad indexing, and that any document which clearly dealt with
two separate subjects should receive entry under both subjects andtherefore we would see no occasion to use the example given aboveof "Machinery see also Patents".
The only way to judge how important c r o s s - r e f e r e n c e s are to theuser is to conduct t e s t s first without and then with their aid. Thiswas done by Swanson in his work on machine indexing (Ref. 17) and
it is the method which we shall be adopting.

F r o m the complete

list of subject headings, we have constructed classified schedules
and, in those searches where, without its use, we failed to find therequired document, we shall repeat the search with the extra aid of
the schedules.
A representative page from the list of subject headings is given
in Appendix C.
The Faceted Classification Scheme
A summary of the principles incorporated in the Faceted
Classification Scheme used for the project can be found in ' C l a s s ification Research Group Bulletin' No. 5, (Ref. 7) and it is notintended here to go into great detail regarding its construction andthe breakdown of the schedules.
Facet analysis is probably the most powerful tool ever to be
introduced into the science of classification and it undoubtedly
provides a most rigorous method for the proper marshalling oft e r m s in a given field.

Its application results in the formation of anumber of conceptual categories, each of which comprises t e r m s
representing i t e m s o f like nature, i . e . t e r m s derived by the application

- 62of a single characteristic.

These categories are then arranged in a'preferred order' so that a proper arrangement of superoifdinate andsubordinate terms is arrived at when a number of terms are selected
and synthesised to represent a complex subject.
The categories of terms derived by this method for the purposeof the project were such as: Aircraft types, Aircraft parts, Engines,
Flying operations, Aerodynamic entities, Forces, Materials,
Processes, etc. These categories were then arranged in that orderwhich it was considered was best suited to the subject field, andterms selected to represent the subject of a document were citedin this order in synthesising a class symbol.
A simple alphabetical notation was used, and for the sake ofbrevity, the base of 26 letters was spread more or less evenly overthe schedules. The notation is not hierarchical except in places where
the breakdown fortuitously makes it so, as the authors of the scheme
are of the opinion that notation need not reflect the hierarchy of theschedules. Each term is represented by a capital letter, usuallyfollowed by one or two lower-case letters.

This provided a fairly

homogeneous arrangement of letters in a class symbol, and seemed
to make such a symbol more manageable than might have been thecase if long runs of either capitals or lower case letters had appeared,or if the notation had been mixed.
The process of classifying consisted of selecting from the schedules
those terms which were relevant to the complex subject of the document
and synthesising the class symbol for the document by citing thenctational elements in the order of the schedules. The subject 'windtunnel tests on blowing over flaps for high lift on short take-off aircraft'- 63 -

would be represented by the following t e r m s :Wind tunnel t e s t sVn

Blowing

Okd

Flaps

Cr

Lift

Nq

High

(Zqn)

S . T . O . Aeroplanes

Bmd

The notation would then be arranged as follows, to give the complete
class symbol for the document :BmdC rNq( Zqn)OkdVn
Except in the comparatively few cases where more than one quite
separate complex subject appeared, a single entry only was made in
the classified catalogue.

The purpose of faceted classification is tofacilitate such one-place classification, and it is evident that theclassified catalogue must be supplemented by some device to enable
access to be made to a given t e r m at every point at which it appears,
regardless of context.

This was achieved by 'chain indexing 1 .

Chainindexing consists of citing the t e r m s represented by the class symbolin the r e v e r s e order of the schedules in order to provide the basic
index entry to the full class symbol for a document, and thereafter
making additional entries by the process of deleting one term at atime from the beginning of the entry and similarly deleting thecorresponding notational element at the end of the class symbol.

The

chain index entries for the above subject would appear as follows :-- 64 -a.

Wind tunnel t e s t s : Blowing: High: Lift:
BmdC rNq( Zqn)OkdV

Flaps: Short take-off aeroplanesb.

Blowing: High: Lift: Flaps: Short take-off
BmdC rNq( Zqn)Okd

aeroplanesc. High: Lift: Flaps: Short take-off aeroplanes

BmdCrNq(Zqn)d.

Lift: Flaps: Short take-off aeroplanes

BmdCrNqe.

Flaps: Short take-off aeroplanes

BmdCr

f.

Short take-off aeroplanes

Bmd

It is evident that all information on "Short take-off aeroplanes" isgathered at Bmd in the classified catalogue. Other t e r m s which are
represented by notational elements further down the class symbol, e. g.
•Blpwing1 - Okd are shown to exist in this context by the chain index
entry (b). In all other cases where 'Blowing' appears, chain index
entries show the contexts and all the 'distributed relatives 1 are thus
gathered under 'Blowing' in the chain index. Such entries may beinspected and entries under the relevant class symbols consulted in thevarious parts of the classified catalogue. Typical chain index entries
might appear thus :Blowing: Air intakes: Gas turbine engines

GfGqOkd

Blowing: Delta: Wings

Cd(Ij)Okd

Blowing: High: Lift: Flaps: Short take-off
aeroplanes

BmdC rNq( Zqn)Okd

In searching for a given subject, the process is as follows:
If the required subject is that shown in the basic chain index entry above(a), the s e a r c h e r examines the chain index under 'Wind tunnel t e s t s 'and may pick out this actual entry by inspection.

This directs him to

the class symbol quoted and entries for this subject appear at that- 66 -should be emphasised that the authors of the scheme were considered
to be the best judges of the form which the structure of the scheme
should take and the method of application of facet principles for thispurpose.

The revision which was carried out was done with this inmind and the approval of the authors was sought regarding all thechanges which were made.
The first changes consisted of minor alterations to correct e r r o r sof a purely technical nature and Mr. Opatowski, the subject specialist,
was responsible for practically all of this work. None of these changes
altered the structure of the scheme in any way.
The first difficulty encountered in the practical application of thescheme arose out of the facility for placing notational elements outof order.

This provision was made because it is evident that no single

order can cater for every requirement, though experience showed thatthe authors' choice of preferred order was probably the best possible.
The type of t e r m most commonly subject to this treatment was thatwhich has valid applications to other t e r m s in many different placesin the schedules, usually for the purpose of adjectival qualification,
though in some cases these t e r m s were of the 'process 1 type and could
conceivably cause ! false drops' if not associated properly with thething to which the process applied.
Initially, any t e r m was regarded as being capable of being placedout of order, provided that it was placed in curved brackets.

Thiscaused difficulty on two counts :a.

Such free movement permitted such inconsistency in synthesisingclass symbols that the purpose of the scheme was largely defeated.

- 67 -

Almost any complex concept could be coded in several different
ways and the choice of combination depended largely on how theindexer would state the subject in words.
b.

Filing order was seriously affected as brackets weresignificant in filing and for a single subject they might appear in one
context and not in another because the one demanded them and theother did not, e. g.
Cd (Ij)Fdb

Spars for delta wings

Cd Ij Nud

Rolling moments of delta wings

Both these problems were largely solved by a decision thatt e r m s in only certain parts of the schedules could be placed outof order, and that these t e r m s should always be bracketted.

The

t e r m s concerned were those at Igb - Iyw, P r b - Px and Za - Zvm.
All these t e r m s a r e either adjectival or a r e the names of generalproperties. Whilst there were other cases where it might be desirable
to place t e r m s out of schedule order, the majority of subjects werestated reasonably satisfactorily by working to this rule, and thenumber of 'false drops' is not expected to be l a r g e .
It was implied in the first instance that when t e r m s were used
in a sense other than that stated in the schedule, e . g . Std used for'sweat cooled', when in fact this is stated as the process 'sweat
cooling', a modified form of wording, e . g . the adjectival form could
be used in the chain index. This facility again lead to inconsistency
in the form of heading in the chain index and it was evident thatstandardisation must be ensured.

There was, at the same time,some doubt about the form certain t e r m s should take in the chain index

- 68 -

entries even when used in their normal context, and it was decided,
therefore, that the schedules be examined thoroughly and a definitive
form for every t e r m laid down. This was done and thereafter nomodification whatsoever of the form given in the schedules was
permitted, even though a slightly different sense was sometimes
produced in chain index entries.

At the same time, an exhaustive

alphabetical index to the schedules was compiled, and the form oft e r m s here followed that of the schedules themselves exactly.
Whilst these steps were fairly rigorous modifications, it wasagreed that no modification to the structure of the scheme had been
made, and the great simplification and consistency which the changes
brought about has undoubtedly justified this course.

This overall

rationalisation, including simplification of the notation by dropping
the original intention to use a hyphen instead of the capital letterfor any second or further elements taken from a given notational
facet (details of which appear in Ref. 7, C . R . G . Bulletin No. 5),
also helped a great deal in simplifying the clerical work of producing
chain index entries.

T h i s procedure became entirely mechanical inthat the typist, after typing the basic entry, formed the second andsubsequent entries by merely removing everything before the firstcolon in the wording of the last entry, and the last notational element.
Notational elements were easily recognised as they always consistedof a group of l e t t e r s , all of which were lower case, except the firstwhich was a capital.

The only exception to this rule was the use of:b and c for bibliographies and charts respectively.
It was felt that the simplification described above was essential
for the practical application of the scheme and experience has shownthat the system has probably gained rather than lost in t e r m s of

- 69 efficiency of retrieval. Nevertheless it seems that some sophistication
might improve the actual arrangement of entries in the catalogue.
One fault which has come to light is that the old problem of 'inversion 1
occurs. The following is an example of this :1. Gf

Gas turbines

2. Gf Hku

Gas turbine combustion chambers

3. Gf Hku Vbd

Design of gas turbine combustion chambers

4. Gf Vbd

Design of gas turbines

It is clear that 4 should have followed immediately after 1 in orderto have the general followed by the general treated specifically,followed by the specific treated specifically.

In other words the designof gas turbines generally should precede material on combustion
chambers and should certainly precede material on the design ofcombustion chambers.
One solution to this problem is to make 'parts 1 of things into
•dependent facets' as are 'parts of rotors and propellers' and to
substitute a symbol such as the hyphen for the capital letter in thenotation, so that we have :1. Dc

Propellers

2. Dc Vbd

Design of propellers

3. Dc - j

Propeller blades

4. Dc - j Vbd

Design of propeller blades

The facility for substitution of the hyphen for the capital letter was
originally provided, but it should be emphasised that its provision was
not for this purpose, and it would in any case have satisfied only thosecases where :-- 70 - •a. the facet was a dependent oneb.

both main and dependent facets were in the same
notation facet

These requirements were met in the second example above, but
not in the first, for it was not permissible to substitute the hyphen
for 'H* to give Gf - ku instead of Gf Hku. It is apparent that a facet
connector of universal application would have met the c a s e , but thescheme is so complex, merely on account of the complexity of thesubject matter, that it is doubtful whether this added complication
could have been justified.
The non-hierarchical nature of the notation caused no difficulty
in indexing, though it might have presented difficulties, from aclerical point of view, if chain indexing had been done up to containing
heads within notational facets.

This latter procedure was not adopted,

though there are some who advocate it. Its adoption would havemeant continuous reference to the schedules by the typist compilingchain index entries and it would have meant indexing combinations oft e r m s which did not actually exist in the catalogue in some c a s e s .
A simple example of this is as follows :Bj Cr Flaps on high wing aeroplanes
If this is fully chain indexed (omitting unsought terms) the
following entries appear :1. Flaps: Control surfaces: Aerofoils: High wing aeroplanes Bj C r
2. Control surfaces: Aerofoils: High wing aeroplanes Bj Cp
3. Aerofoils: High wing aeroplanes Bj Cc
4. High wing aeroplanes Bj

- 73 -intercalated between them, and the wording in the chain index
entries assumes the same form in reverse order, e.g.
Fr Nbk Nep Nvk Pressure grad: Shear flow: Supersonicflow: ConesFr Ned Nfk Nvk Pressure grad: Boundary layer: Laminar
flow: Cones
Fr Nhd Nfk Nvk Pressure grad: Boundary layer: Shockwaves: Cones
Fr NvkPressure grad: Cones

This situation demands that every entry under pressure gradient must
be examined, in case the two terms appear, for though other terms
may exist between them in the index, they may be irrelevant as far
as the search is concerned, and any such entry may refer to a
useful document.
These are anticipated difficulties with regard to searching andmay prove l e s s severe than seems to be the case at present.

In anycase chain indexing is not necessarily the best way of taking advantage
of a faceted classification scheme, and it is obvious that whenever thelest-mentioned problem occurs (that of combinations of terms), there
is no other satisfactory or economic method but mechanised sorting.
Once the initial difficulties of ensuring consistency and standardisation of terminology, and of simplifying the clerical work of chainindexing had been solved, the scheme was quite simple to use fromthe point of view of indexing.

These difficulties were, in any case,of no greater magnitude than could reasonably have been expectedwith a completely new classification scheme.
The main outline of the facet schedules and the full schedules fora section of Aerodynamics are given in Appendix D.

- 74

Uniterm
The Uniterm System of co-ordinate indexing is such a simple
scheme that there is little to report as far as experiences on the
project is concerned.

Whilst the system is simple in practice, theprinciple of subject analysis is j ust as relevant here as it is withany information retrieval scheme, but, as discussed e a r l i e r , thesystem has been used in its present form for the purpose of comparing
the result of indexing based on f literary warrant 1 with the moresophisticated methods of analysis such as that provided by facet
classification.
Initially the three indexers were allowed to compile independent
lists of uniterms and this procedure was continued until the end of
the indexing of the first 6,000 documents. At this stage the three
independent lists were integrated and problems of synonyms andcross-referencing were resolved.

Up to this point, conventional

posting of t e r m s had been carried out, but it was decided that posting
could be done more economically by assigning simple numbers to thet e r m s and recording these, together with document numbers on Powers
Samas punched c a r d s .

Synonyms were catered for, by simply assigning

the same Uniterm number to all t e r m s in a group of synonyms.
The use of punched cards will provide indexes in two forms:(a) The punched cards themselves form one index and searching
can be done by keeping the cards in Uniterm number order, andfeeding one block of cards bearing a common Uniterm number
against another similar block, into the collator, and seeking
coincidence of document number.
(b) The cards will be fed into the interpreter having been

- 75 -

sorted into (1) Uniterm number and (2) document number
within batches bearing the s a m e Uniterm number.

Thei n t e r p r e t e r will then print out l i s t s in this o r d e r , providing
a conventional v i s u a l Uniterm index.

Suitable p r o g r a m m i n gwill provide for posting in t e r m i n a l digit o r d e r .
The only problem which a r o s e in the indexing was the c o m m o none of how far to go in splitting down concepts into 'unit t e r m s * .

It

s e e m s i m p o s s i b l e in the present state of knowledge to lay down
specific r u l e s , and as with alphabetical subject cataloguing, g e n e r a l
usage i s probably s t i l l the best guide.

The vast majority of t e r m s

c a u s e no p r o b l e m , but compound t e r m s in c o m m o n use are not s oeasy.

'Turbojets' and f Turboprops ! are c o m m o n l y u s e d , but'Turborockets' i s not.

Should we split the latter into 'Turbines 1 and'Rockets' and if s o , should we treat 'Turbojets' and 'Turboprops' inthe s a m e way ?

'Engines' provides no p r o b l e m , but how do we c a t e r

for the s e a r c h e r under ' P o w e r plants' ?

F o r the purpose of the

project the c o m m o n l y used compound t e r m s w e r e used in t h e i r
usual f o r m , e . g . 'Turbojets', e t c . and where t e r m s did not appear
in this form in the l i s t , the compound t e r m was split into i t s c o m ponent t e r m s .

The first appearance of a difficult t e r m resulted in

a d i s c u s s i o n and a d e c i s i o n by the i n d e x e r s .

No s e r i o u s difficultya r o s e as a result of this p r o c e d u r e , and t h e r e was usually no needfor recording such d e c i s i o n s , as the i n d e x e r s ' p e r s o n a l knowledge
was adequate to avoid different t r e a t m e n t s at different t i m e s oftroublesome t e r m s .
A difficulty which i s always probable with U n i t e r m i s the l i k e lihood of 'false drops' b e c a u s e of two or m o r e t e r m s being unintentionally related.

A s i m p l e example i s the coding of a document onthe 'vibration of helicopter rotors'.

If these terms 'vibrationt.

'helicopters1, 'rotorst a r e used, then if a search is made for documentson 'vibration of helicopters induced by rotore', the former document
will be eetrieved, though the subject is not the same. There is someargument about the eeriownees of such 'false drops', and the results
should provide some fairly conclusive evidence on this point.
Another problem which appeared was that of the document whichcontained material on more than one distinct subject. All the uniterms
were posted to the single document number, and it is evident that this
could a160 came 'false drops'.

The solution to this would obviously

be to assign more than one number'to such documents, in order thateach subject concept can be isolated and identified by a unique number,but the seriou6neer of this problem will depend on how much common
ground exist6 between the eeparate subjects in the document. Again,
the test6 will show whether any such special provision ie justified.
T h e n was no doubt that uniterm was quite the simplest of thefour systems to apply. Whether it loses in difficulty of retrieval
what ie gained in simplicity in indexing. remains to be seen.
A representative page from the list of'uniterme is given in
Appendix E.