DiCoMo: A cost estimation model for digitization projects

poster / demo / art installation
  1. 1. Alejandro Bia

    Libraries - University of Alicante

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DiCoMo: A cost estimation model for digitization


University of Alicante


University of Tübingen







The estimate of costs of a digitization project is a very difficult task, to
say the least. It is difficult to make exact estimates beforehand due to the
great quantity of unknown factors. However, the common practice when signing
digitization agreements is to set a firm commitment before beginning the
works so much concerning economic costs as in terms of time lapses and
deadlines. In the same way as for software development projects an incorrect
estimate of times and costs produce delays.
Based on methods used for cost prediction in Software Engineering like CoCoMo
(Constructive Cost Model; Boehm, 1981) and Function Points (Albrecht, 1981),
and using historical data gathered in almost three years of existence of our
digital library, we have developed a model for digitization cost estimates
(DiCoMo, Digitization Cost Model) for text digitization projects in general.
This method can be adapted to different production processes, like the
production of digital texts using scanning plus OCR and human proofreading,
or the production of digital facsimiles (scanning without OCR). The estimate
done a priori is improved as the project evolves by adjustments done with
real data obtained from previous stages. Each estimate is a refinement
obtained as a result of the work developed so far.

Factors that affect digitization costs
There are many factors that affect the cost of production of a digital
object. Both these factors and their effect on costs are difficult to be
determined and have to be carefully studied. Among them, we can highlight
the individual capacities of the persons assigned to the project and their
familiarity with the specific characteristics of the work to be digitally
published, its complexity, size, demanded level of quality, the technology
used and the familiarity with the computer tools to be used.
Main Factors that influence digitization costs:
Size of the material to publish
Complexity of the task
Individual capacity of editors, correctors and scanner-operators
Special quality requests
Technological level of the environment

The assigned time impacts mainly in the quality of the product obtained which
is notably lowered when the times assigned are unreally short and they force
the technicians to work under excessive pressure. This is particularly true
for the correction and editing process, where text output from OCR has to be
carefully proofread and corrected. This is a delicate craft that takes time
and cannot be done under excessive pressure since when it is not properly
done obliges to further revision and corrections that have a very negative
impact on costs with a final result that turns out to be worse than the time
initially saved. Next each one of these factors is described.

Size of the material to publish
Digitization projects, compared to software design projects, have the
advantage that we know beforehand the size of the work to be done (namely
the number of pages or words to digitize).
The first and easiest way to determine the raw size of a text to be digitized
is to count the pages. But pages are not equally dense for all books. We can
have an approach to the density by counting the words that fit in a standard
page, or the words that fit in a fixed size window, and then assuming that
the rest of the pages are similar in this respect.
To count individual words would be more accurate, but not a practical
approach at all. Anyway, after the OCR process takes place we will obtain a
text file, with errors of course, but nevertheless a text file where we can
automatically count the number of words or the size in bytes to have a
better measure of the amount of proofread and correction work that comes
ahead. So this second measure of the size serves to adjust the initial
estimates for higher accuracy.

Complexity of the task
This is by far the most significant modifier concerning cost estimates. In
fact, there are many complexity factors that affect each stage of the
development process. In the case of the correction stage, which we consider
the most critical one, there are various factor to take into
the type of text (prose, verse, drama written in prose, drama
written in verse, dictionary)
footnotes if the number is too high
quotations in foreign or classical languages (if too many)
the complexity of the author style and vocabulary
the quality of the OCR output (few or lots of errors)
the legibility of the paper copy used as original

Concerning markup, complexity varies according to the number and difficulty
of the tags to added. Drama, for instance, with the need of a castlist, speaker and
speeches, requires an additional tagging
effort. Verse with split lines is another case of added complexity since
special care needs to be taken to assign attribute values to declare which
part (initial, middle, or final) of the split line of verse is which.
In the case of the production of digital facsimiles from manuscripts, a case
of extra complexity is when we have to work on rare and valuable originals
that have to be handled with special care (wearing rubber gloves for
instance) and using a digital photographic camera instead of a flat bed
scanner. On the contrary, digitizing unbounded pages using a flat bed
scanner with automatic page feeder would be the easiest case.

Individual capacity of the technicians
In the computer programmers world, individual productivity has been measured
extensively. Harold Sackman and collaborators, carried out an experiment in
1968 where they made evident that performance differences registered in
individual programmers were much bigger that those attributed to the effect
of the working environment. The difference between the best and the worst
performance was very high, being the experience a decisive factor. In a
later experiment, Sackman observed a variation in the productivity of as
much as 16 to 1 (Sackman, 1968). DeMarco and Lister also discuss the effects
of a well integrated group to enhance productivity in their book Peopleware
(Demarco+Lister, 1987).
Now back in the field of electronic editing, the results that we have
measured comparing correctors performance in tasks of correction of texts
output from OCR show us differences in productivity of as much as three to
one, depending on the individual ability and speed of correctors. Variations
in productivity of this magnitude are significant for cost estimates, so
including a parameter to adjust the estimates according to individual skills
seemed to be necessary.

Special quality requests
Producing a modernized digital edition from an ancient text takes additional
time and effort compared to processing a modern text, since modernization is
a complex task that involves difficult decisions. Using Madison markup for
the transcription of a manuscript is another example of additional requested
complexity. So is the case of making high legible digital facsimiles of
ancient manuscripts, where special care and fine-tuning of the scanning
properties may be needed.

Technological level of the environment
This is a relevant issue when using different technologies or migrating from
old to new production tools. When the environment is stable and well known,
and the estimate equations are well adjusted for it, there is no need to
care of this issue. Changes in technology, however, will surely requiere
modifications to the equations.

Cost estimation models
According to R. Fairley (Fairley, 1985), inside most organizations, the
estimation of production costs is usually based on past experiences.
Historical data are used to identify the cost factors and to determine their
relative importance within the organization. The above-mentioned, is the
reason for current project's production costs data to be stored for later
We can classify cost estimation methods in two broad categories depending on
whether the approach goes from the general to the specific (top-down) or the
other way around (bottom-up). Top-down models first consider the costs at
the most general level, being usually based on the exam of the costs of
previous similar projects. Bottom-up models first consider the development
cost of each module which are then added to obtain the total cost. This
technique concentrates on the costs associated with the independent
development of each module or individual component of the project and we
believe that it is the most appropriate for digitization projects of
literary works. It can lead to errors if the time spent in some parallel
tasks like version control, backup copies, digital preservation and quality
control is not taken into account. The bigger the project, the more
important these factors become.

Expert judgement
A top down technique frequently used to estimate costs is based on expert
judgement. Expert judgement is based on experience, on previous knowledge
and on the commercial sense of one or more individuals inside the
organization (Fairley, 1985). According to Fairley, the biggest advantage of
expert judgement which is experience, can end up being its weakness. The
expert can trust that a project is similar to a previous one, but it can
happen that he/she has forgotten some factors that make the new task
significantly different. To compensate for this, and for a possible lack of
experience in a particular project type, a group instead of individual
experts are used to try to arrive to a consent. The purpose is to minimize
individual flaws and the lack of familiarity with some kind of projects,
neutralizing personal tendencies.

The DELFI method
The DELFI method is a group expert judgement method that tries to minimize
the interpersonal influences in a groups that may spoil the final
estimation. The DELFI technique was developed at the Rand corporation in
1948, with the purpose of obtaining the consent of a group of experts
without having the negative effects of group meetings (Helmer, 1966). This
technique has been adapted to estimate costs in the following way (see
Fairley, 1985):
1. A coordinator gives the documentation with the description of
the project to each expert and a form to write his/her estimate.
2. Each expert studies the definition and anonymously determines
his/her estimation. The experts can consult the coordinator, but not
another expert.
3. The coordinator prepares and distributes a summary of the
estimates done so far.
4. The experts carry out a second round of anonymous estimates,
using the results of the previous one. In the case that an estimate
differs much from the others, an anonymous justification by the
expert that made it may be requested.
5. The process is repeated as many times as it is considered
necessary, avoiding group discussions.

It is possible that after several rounds of estimates there is no consent. In
this case, the coordinator will study the causes of such disagreements and
try to solve the differences, sometimes by adding new information.
In our case we have preferred not to use this type of expertise based
estimation methods, but to take advantage of the expert knowledge to
determine the factors that have a significant influence on production times.
For digitization costs estimation we preferred to use bottom-up methods,
preferably algorithm-based ones, as we explain below.

Work break-down structures
Work breakdown structure or WBS, is a top-down method that helps to plan a
project. A work breakdown structure is a hierarchical flowchart where the
different parts of a project are established reflecting a hierarchy of
products and processes. A WBS flowchart of processes identifies the work
activities and their interrelations. Using the WBS technique, the total cost
of the project is calculated by adding the costs of the individual
components in the flowchart.

Algorithm based cost models
With algorithm-based cost models the costs are calculated by adding the costs
of each of the modules or subparts of the project in a bottom-up fashion.
The constructive cost model or COCOMO is a cost model based on algorithms
described by B. Boehm (Boehm, 1981).
According to Pressman (Pressman, 1988), the equations for Basic-COCOMO are
the following:
E = a KLOC^^b

M = c E^^d
where E is the effort applied in
persons-month, M is the development time in
chronological months, and KLOC are the estimated
number of lines of code (in thousands). The factors a, b, c and d are from a table given by B. Boehm. This values are
for estimating software production costs, and are irrelevant for our
purpose. We will only take the spirit of COCOMO and adapt it to estimate
digitization costs.
Intermediate-COCOMO takes the following form:
E = a KLOC^^b EAF
where a new effort adjusting factor
is added. This factor is obtained by first evaluating a set of complexity
factors and then extracting the value EAF from a table. Basically, EAF is a
value close to 1 that adjust the resulting effort calculation according to
the overall complexity determined by various features of the project. Is
usually a value between 0.70 and 1.65.
In our digitization cost model (DiCoMo), we use a basic equation similar to
Basic-COCOMO, but with an added fixed value f:

H = a P^^b + f

We do not have to estimate the size (in pages) P
which is known beforehand. We directly calculate the number of hours H. We add a fixed value f
which stands for the fixed time necessary for the type of task considered,
independent of the size of the task. An example of this is the time needed
to adjust the scanning software parameters, which is a fixed time which does
not depend on the number of pages to be scanned later.
For an example of this Basic-DiCoMo approach, see figure 1, where an
estimation curve (thick line) approaches real data spots (black squares)
that represent real measures from the correction stage. The thin straight
line represent a linear approach to the spots, while the curve represents
the following estimation equation which gives us the estimated number of
hours to correct a text given the number of pages:
H = 0.0653 P^^2,091 + 8

Figure 1: Correction-process data for July 2001 (Hours
vs. Pages).

For instance, a standard-complexity book of 100 pages will take about 59
hours of correction and markup according to this estimation.
This simplistic approach doesn't take into account the fact that different
literary works have different degrees of difficulty at the time of
proofreading. This differences in complexity is due to several facts. We
have detected the most important ones and added a complexity adjustment
factor c which leads to our Intermediate-DiCoMo equation:
H = a c P^^b + f

Procedure for the estimate of costs using DiCoMo

1. identify all the subprocesses and all the units (books or other
literary works) to be processed.
2. measure the size of each unit and establish the production steps it
will undergo from the corresponding processing workflow.
3. specify the complexity factors for each unit..
4. calculate the time each unit will take, as the sum of the estimated
times for each production step it will undergo (use the adequate
equation for each step together with the corresponding complexity
5. calculate the total time of development for the project.
6. compare the estimate with another, perhaps a top-down one like the
DELFI technique or expert-judgement, identifying and correcting the differences
in the estimate.

This version of DiCoMo is a simplified equivalent of the intermediate COCOMO
model (Boehm, 1981) used for software development estimates adapted in this
case for digitization project estimates.
Many studies have attempted to relate size oriented methods like COCOMO and
function oriented methods like function-points
(Albrecht+Gaffney, 1983). We take from the function points model of Albrecht
(Albrecht, 1981), the idea of modularization according to functions. In our
case we consider each production step a functional unit, for which the
estimation equation is applied.

We have designed a cost estimation model for digitization projects based on
known software engineering cost models. These methods allowed us to predict
the overall time a digitization project would take within a 20% error range.
Digitization projects, compared to software design projects, have the
advantage that we know beforehand the size of the work to be done (namely
the number of pages or words to digitize). In software engineering we can
only guess the total number of lines of code or function points a project
will take, and the certainty of the cost estimates will depend largely on
this preliminary size estimate.
We verified that the model we propose works well in practice, and can be
easily applied to different digital production processes, but the cost
equation needs to be fine-tuned in advance for the model to be applied. This
requires two things to be done first: on one hand the main objective factors
that affect the time required to do the work must be determined and weighed,
and on the other hand sufficient historical data must be gathered to
fine-tune the parameters of the cost equation. Having this information a
cost-equation for the specific production process is easily obtained.
Good expert knowledge of the process facilitates the fine-tuning task and
allows for better estimation equations. Nevertheless, the cost-equations can
be dynamically improved by re-adjusting the parameters with the new data
fed-back from new projects. In this way the estimation model can be
incrementally improved.

The production process of digital text books.

The production process of digital facsimile

Automatic transformation: the one-source many-uses

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Conference Info

In review

"New Directions in Humanities Computing"

Hosted at Universität Tübingen (University of Tubingen / Tuebingen)

Tübingen, Germany

July 23, 2002 - July 28, 2008

72 works by 136 authors indexed

Affiliations need to be double-checked.

Conference website: http://web.archive.org/web/20041117094331/http://www.uni-tuebingen.de/allcach2002/

Series: ALLC/EADH (29), ACH/ICCH (22), ACH/ALLC (14)

Organizers: ACH, ALLC

  • Keywords: None
  • Language: English
  • Topics: None