Intelligent Information Management, 2012, 4, 269-276
http://dx.doi.org/10.4236/iim.2012.425038 Published Online October 2012 (http://www.SciRP.org/journal/iim)
Supply Chain for Regional Centralized Purchasing:
An Application Model
Alessandro Pepino, Marcella Rovani, Adriano Torri, Mario Sansone
Department of Biomedical, Electronic and Telecommunication Engineer ing,
University of Naples “Federico II”, Naples, Italy
Received September 3, 2012; revised October 5, 2012; accepted October 14, 2012
In Europe Health Organizations are progressively modifying their management models to rationalize expenditure in
order to assure better levels of effectiveness and efficiency: many countries are going to centralize the management of
goods and services supply. In this paper a specific model of centralized purchasing is proposed; it is particularly suitable
in cases of severe economy suffering at regional level (e.g. Campania, Lazio, Calabria in Italy) or at national level (e.g.
Greece, Ireland, Italy), that means in all those cases where the scale economies, obtainable by supply centralization,
would be partly or totally compromised by the extra charges induced by the missing of contractual commitments. This
work aims either to analyse such specific approach for centralized purchasing or to propose a simulation model based
on Petri net, which could be useful for designing and managing similar case studies.
Keywords: Centralized Purchasing; Workflow Management; Health Information Systems
In the last 20 years in Europe, Healthcare Organizations
are progressively integrating, at regional level, their
workflows in order to guarantee adequate health services
despite the limited financial resources in comparison
with population healthcare needs [1,2].
Especially, many regional and national administrations
aim to integrate and centralize in a single body, under
public supervision, all the activities that can be assimi-
lated each other that are normally carried out, with more
expenses, by few peripheral body that in the following
we indicate as “Public Health Companies” (PHC) which
in general are public organizations responsible for the
health services (and all the related activities) concerning
one local district located within the national/regional
By instance, one centralized organization (normally a
public company) for goods and services procurement,
allows significant savings as well as good quality; there-
fore, in these last years, the pharmaceuticals and medical
devices purchase processes have been centralized 
either in several Italian Regions and also abroad [4,5].
These centralized procurement bodies, in the most cas-
es, are responsible just for the procurement competition,
in order to increase quantities and reduce goods and ser-
vice costs; the PHC remain normally responsible for the
supply chain and especially for the payment to the sup-
In some cases, where the PHC are not able to meet
contractual commitments because their heavy debt, these
central bodies keep in charge also part of the supply
chain (order-invoice-payment) on behalf of the PHC in
order to meet agreement payment time.
This paper describes a model of a Regional Purchasing
Agency that integrally manages the whole procurement
process. This paper analyses the process from the work-
flow point of view  and suggests a specific model,
based on Petri Nets, in order to quantitatively outline
benefits and critical points.
2. Materials and Methods
In the case study here presented, the Regional Purchasing
Agency is responsible for drugs and medical devices
purchase to be distributed among healthcare public com-
panies responsible for the regional districts that in the
following will be indicated as “PHC”.
At an operative level, the workflows could be outlined
as shown in Figure 1.
Periodically the Agency collects from the PHCs the
data concerning the Health Regional Districts needs, and
then announces the centralized procedures of bids
evaluation concerning the acquisitions of required goods
and services. After that, the PHC—on behalf of and
through the Purchasing Agency information system-send
opyright © 2012 SciRes. IIM
A. PEPINO ET AL.
Figure 1. Regional purchasing agency workflow.
the orders to those suppliers who have been awarded,
through public competition, on the basis of agreement
prices and supply conditions. The Suppliers send goods
and shipping documents to PHC and the corresponding
invoices (that will be indicated in the following as “pas-
sive invoices”) to th e Regional Agency itself. Finally the
Regional Agency either provides payment to the supplier
or attends to issue corresponding active invoices to the
Public Health Companies, at the end of accounting cycle.
The Public Health Companies will not provide any pay-
ment to the Regional Agency but they are responsible for
the receipt and the logistics of supplied goods, as well as,
the shipping documents checking, that is a mandatory
requirement for the passive invoices’ payment to the
On the basis of one specific agreement with the Re-
gional Administration, the payment of the active invoices
to the Regional Agency by PHC is made through a spe-
cific mechanism of withdrawals, from the funding that
the Regional Administration periodically send to the in-
dividual PHC; this mechanism represents an essential
element of guarantee for the Regional Agency and, there-
fore for the Creditor Suppliers, too.
This specific operating model, which is different from
the one adopted by the most of the Purchase Regional
Agencies in Italy, generates a duplication of the adminis-
trative flow; in fact, for any provision, two corresponding
invoices must be individually processed by the Regional
Agency (Public Healthcare Company <-> Regional A-
gency <> Supplier); this peculiarity represents a critical
element that necessarily imposes that the documental
flow and the management model, starting from the order
up to the invoice’s payment, should be as much auto-
mated as possible. So, the Regional Agency has to set up
an appropriate administrative information system, which
should be able to manage, for a huge amount of docu-
ment (200,000 order/invoice per year), the great hetero-
geneity of deliveries and th e different invoice modalities,
normally specified into the agreement with the different
2.1. The Information Management System
The Information System has to manage the whole ad-
ministrative workflow; with reference to a usual account-
ing management system , it must also provide a spe-
cific set of check points and management functions re-
lated to the specific n eeds of the Reg ional Agen cy supp ly
chain. The workflow reported in Figure 1 highlights the
high degree of integration that is required between the
information systems operating in the PHC and the Cen-
tral Agency. Moreover, it also should comprise integra-
tion’s modules with the local information systems han-
dled by the individual PHC’s. The PHCs are in fact re-
sponsible for the certification of good’s conformity, and,
in addition, must have their own independent accounting
system in order to guarantee an appropriate internal
So, the information system integration’s modules must
The order database update to keep aligned the orders
managed by the PHC and the corresponding orders
generated into the Regional Agency’s Centralized Sy-
The shipping documents database update to keep
aligned the shipping document managed by the PHC
and the corresponding shipping document database
into the Regional Agency’s Centralized System, in
order to allow the staff Agency to authorize the in-
From a technical point of view, in the Author’s ex-
perience, the integration between the central information
system and the PHC one, could be done by mean a sim-
ple FTP data exchange [8,9], although Web services and
SOA technologies promise to be more efficient from this
point of view .
The information system should allow the PHC opera-
tors to make via web a “proposed order”, representing
the Health Company’s request to the Regional Agency,
which then has to be confirmed before delivering to the
Normally, all these activities are carried out by PHC ad-
ministrative staff under the supervision by one pharma-
cist/administrative belonging from the Regional Agency)
in order to complete su ch “ordering phase”.
The latter, as holder of the supply contract, sends
(automatically by fax or by mail) the order to the supplier;
of course, the same order, thro ugh the integratio n system,
Copyright © 2012 SciRes. IIM
A. PEPINO ET AL. 271
has to be exported to the PHC Information System.
The PHC operators, at the good receipt, must provide,
in their information systems, the data entry concerning
the details about the received products; after that these
data must be exported as well, toward the Regional
Agency information system.
The Regional Agency has to register the passive in-
voices sent by the Supplier. In principle the passive in-
voices recording usually requires a simple data entry
concerning few key data (Figure 2).
On the other hand the generation of the active invoices
requires full detail of the order rows. This means that,
given the expected document volume, (200,000 docu-
ments/year), in the case of passive invoices manual data
entry, this would resu lt in a heavy workload and a poten-
tial quality data loss, su ch as to make the model not suit-
If the model of e-invoicing scheme would be already
gone in Italy, the problem would be already solved, but,
unfortunately, most of the supplier cannot yet provide
electronic invoices. One possible solution, to avoid ma-
nual data entry, is to reconstruct th e details of the passive
invoice document by using the data contained in the ship-
ping document normally updated by the PHC upon re-
ceipt of the ordered goods or services.
As reported in Figure 2 on the basis of the order num-
ber and the Supplier code, it could be possible to find—
through the table of the shipping documents (CMR)—
the details related to the passive invoice; this mechanism
therefore allows to automatically generates an “accounted
Figure 2. Invoice details reconstruction.
invoice” (that is line by line coherent with the passive
invoice) avoiding the manual data entry. Of course a
number of checks in order to verify the exact match be-
tween the accounted invoice and the shipping document
has to be done .
Unfortunately, sometimes, at the time when passive
invoice is recorded in the information system, the data
concerning the shipping documents are not yet available
because they have not yet been inserted in the PHC’s
database; moreover the unit cost, or the description of the
goods on the invoices maybe different from the ones
contained in the shipping document, due to a database
In such cases, the accounted invoice details must nec-
essarily be registered manually; small differences due to
numerical rounding however can be tolerated according
to the limits prescribed by law; this allows to avoid, in a
significant number of cases, the manual data entry and
therefore it makes more efficient the operating flow.
On the basis of accounted invoice the information sys-
tem should generate, through an automatic overturning,
the correspondin g active invoices, to be sent to the PHC,
in order to be accounted in the respective budgets. The
last step of the management cycle requires the compari-
son between the passive invoice and the shipping docu-
ments already registered into the information system, in
order to authorize the payment to the supplier; in this
step that is under the responsibility of the regional agen-
cy, the Regional Agency staff should check, line by line,
the exact match between the ordered products, and ones
delivered and billed. This activity is generally quite hard-
working, but, of course, in the case that the accounted
passive invoice has been generated by the automatic
procedure, this check could be automatic as well. From
the above, it is importan t, in order to reduce the worklo ad
and therefore the operating times (also for improving the
overall quality of the process), to have an adequate align-
ment of the product codes that are used at the order’s
time, to ones used by suppliers.
In other words, the correct and efficient management
of the entire sup ply chain order - DDT - invoicing - p ay-
ment, generally requires an accurate alignment of data
related to the product codes, with the ones reported in the
order and in the invoice documents, in order to allow an
easy and reliable comparison of the invoices, order and
So, it is very important to ensure the consistency be-
tween the counterparts data provided to the following
Products code of Health Organizations,
Providers’ product code,
Medicine and medical devices’ code,
Copyright © 2012 SciRes. IIM
A. PEPINO ET AL.
Copyright © 2012 SciRes. IIM
generation of a further document which will be ind icated
as OF (Figure 4). The Suppliers deliver the required
products, with the relative shipping documents, directly
to the PHC Thus, the latter must manage the logistic ac-
tivities that are necessary for the distribution to the des-
tination PHC departments and must verify the conformity
of the receipt goods. Once the order has been sent to the
supplier, the workflow provides (AND split) two distin ct
parallel branches: the first, who belongs to the Agency
for the management of the passive and active invoices
(Figure 5); the second who belongs to PHCs, who have
in charge the logistics, that includes the management of
the shipping documents (Figure 6).
Any misalignment between these tables may become a
discrepancy or ambiguities in the comparison between
the order rows and the invoices data. From this discrep-
ancy arise both the difficulties in payment authorisation
and consequently delays in completing the pro cedure.
2.2. A Supply Chain Model Based on Petri Nets
On the basis of the above steps the supply chain man-
agement should take into account a number of efficien-
cies/inefficiencies which arise from the workflow struc-
ture and from different actors in the process. This second branch provides also—on the basis of
what really happens—two alternatives: in one case the
goods and the shipping documents are regularly and
quickly handled, (CMR collect branch); instead, in the
other case, the shipping documents—because a number
of reasons related to the inefficiency of the healthcare
companies’ logistic network—follo ws an alternative path
where the same activities are carried out in a much
longer time (CMR Lost branch). The two branches are
then joined by an AND join that simulates the positive
check of compliance necessary for the invoice payment
In order to investigate the above supply chain, and to
provide a simulation tool for such organizational model
that could be used also for further case studies, we have
designed a workflow based process model by using the
Petri nets. As shown by the literature  the Petri nets
allow to design a process specifying the activities se-
quence and assigning them a duration time and the re-
sources who are delegated to their execution.
Once the net design has been completed, some simula-
tions can be done to reproduce the process behaviour in
different conditions, in order to highlight the critical is-
sues. The invoicing process involves sequentially the re-
cording of the passive invoices sent from the Supplier to
the Regional Agency, then the generation of an active
invoice from the Regional Agency to the PHC who per-
formed the order. The model provides that all these ac-
tivities may happen in a manual or automatic mode: in
the first case the registration of the individual rows of the
invoice must be performed through a manual data entry;
in the second, assuming that both the order and the ship-
ping document are available in electronic format, the
reconstruction of the individual rows of the invoice can
occur automatically (Figure 5). Then, the correct han-
dling of the shipping documents is involved in the proc-
ess at two levels: directly regarding to the compliance
Figure 3 shows a Petri net, based on the operative steps
above outlined, that, without any claim of completeness,
allows to simulate the main critical elements of the sup-
ply chain workflow concerning the Regional Purchasing
Following the Petri net’s rules the network’s token
represents, within the workflow, the document of order/
delivery/invoice; in particular, it is assumed that one to-
ken corresponds to n. 200 orders/shipping documents/ in-
voices. In these circumstances the flow starts with the
order generation by PHC (through Regional Purchasing
Agency Informatio n System). Th ese orders will be b elow
indicated as OA. They are then forwarded by the Re-
gional Purchasing Agency to the Suppliers through the
Figure 3. Complete petri net.
A. PEPINO ET AL. 273
Figure 4 Ordering phase.
Figure 5. Invoicing management.
Figure 6. Shipping document management.
check, and indirectly through the ability to automate the
passive and active invoices’ rows entry in the informa-
Similarly, a last segment of the model simulates the
payment authorization process: it can be carried out ma-
nually—through the manua l verification rows by rows of
the shipping document associated with the order—or au-
tomatically, thanks to invoice reconstruction above de-
tailed (Figure 7). Because the automatic invoice man-
agement depends on the number of shipping documents
in time recorded, all these different operating situations
are represented, within the model, through a series of
“xor” transitions that shunt, alternately, in appropriate
branches the token on statistical basis, depending on the
percentage of transport document which have been prop-
erly handled (X.miss).
In order to have workflow simulation, each transition of
Petri Net must be configured with the associated resources.
For the model configuration—as shown in the Table 1—the
data to be measured on the real system are, therefore:
1) X.miss: percentage of documents managed with
considerable delay, that is conventionally assumed equal
to 20 days instead of 3 days;
2) N. Inv: n. purchasing staff unit of the Regional Pur-
Copyright © 2012 SciRes. IIM
A. PEPINO ET AL.
Figure 7. Payment authorization phase.
chase Agency responsible for invoices and payments
3) T. Inv: Time required to load 200 passive invoices
by a personnel unit; this data is conventionally fixed
equal to 5 days/staff unit;
4) N. Paym: N. Agency’s staff unit responsible for
managing invoices and payments;
5) T. Paym: Time required for authorize the payment
of 200 passive/active invoices by one staff unit; this d ata
is conventionally fixed at 7 days/staff unit;
6) N. cmr: N. of PHC’s unit responsible for shipping
7) T. cmr 1: Average time of management’s collection
of shipping documents (great channel); relating to 200
invoices/ shipping do cuments, this data is conventionally
fixed equal to 7 days/staff unit;
8) T. cmr 2: average time of management’s collection
of shipping documents (delayed channel); referring to
200 invoices/shipping documents; this data is conven-
tionally fixed equ a l to 20 d ays/ staff unit;
9) T. cmr 3: Average time of compliance verification’s
management; referring to 200 invoices/shipping docu-
ments this data is conventionally fixed equal to 1 day/
It should be pointed out that while the values 1), 2), 3),
4), 5) are determined on the basis of authors’ experience
inside one regional agency’s activities, the setup of 6), 7),
8), 9) should be done on the basis of PHC’s indication
concerning the specific case study.
Anyway, a more accurate estimation of this informa-
tion would not change significantly the model. In the tab.
1 are listed the values so assigned to the configuration’s
It is interesting to analyse the model’s behaviour as a
function of the parameters on which the Regional Pur-
chasing Agency has some responsibility. We consider
that the Regional Agency’s management could change
“N. inv” or on “N. Paym” increasing the staff for invoice
recording and payment authorisation. Alternatively, it
would be also possible to modify “X.miss”, through ap-
propriate actions on the PHC management in order to ask
them more attention about the shipping document man-
agement. About all the other parameters, conversely, it’s
far more complex to step in, because they are completely
under the responsibility of the PHC Administration.
By using the Woped analysis tool we aim to demonstrate
what are the strengths and the weakness characterizing
the workflow model designed for Regional Purchasing
Agency PHC. Such inefficiencies, especially referring to
the shipping document’s management, therefore influ-
ences the entire operative work flow. The workflow model
has been designed by the open source software www.
woped.org ; the related file is attached to this paper.
Into the Woped quantitative analysis menu, by setting the
parameters of resources’ flow and productivity referred
to point 1) to 7), it is possible to evaluate the workflow
duration which could be considered as the payment time
“p. delay”, that represents one major priority of a Re-
gional Agency that carries out the central role of pay-
In particular, our analysis, evaluates the trend of th e “p.
delay” as a function of the following variable elements:
1) percentage of missed shipping docum ents “X.mi ss”;
2) amount of resources used for the invoices and pay-
ment management “n paym”, “n. inv”.
In the Table 2 they are listed the parameters required
by the software simulation with reference to the pre-
su med work volume.
As far as the point 1, we report on the Table 3 and in
the Figure 8 the results obtained by some simulations
performed considering different values assigned to the
percentage of “X.miss” (missed shipping documents).
As expected, the payments timing is drastically re-
duced by the “X.miss” reduction of thanks to the conse-
quence of the accounting workflow automation im-
provement; this aspect is expressed in the corresponding
branches in the model marked with (X.miss – 1). It
Table 1. Configuration parameters.
Min. Value Max Value Fixed Value
X.miss 10 90
N. inv 4 9
N. cmr 12
N. paym 4 6
T. inv 5 days
T. paym 5 days
T. cmr1 7 days
T. cmr2 20 days
T. cmr3 1 day
Copyright © 2012 SciRes. IIM
A. PEPINO ET AL. 275
Table 2. Simulation parameters.
Value of each token 200
Number of token in one simulation 1000
Invoces number 200,000
Observation perio d 1 year
Time unit 1 day
Table 3. Payment delay vs X.miss.
X.miss % P. Delay (day)
Figure 8. Payment delay respect to the shipping document
should be considered, however, on the basis of the real
experience—that it is not easy—relay on a reduction of
“X.miss” < 50%; therefore, it was made a second simula-
tion in which the percentages of the xor branches it has
been assigned a value of “X.miss” equal to 50%.
So, the simulations were carried out according to the
data of the Table 4 . In this simulation, given the value of
X.miss = 50% the payment time is calculated, firstly by
increasing (N. inv = 4 to 9) the resource staff who is re-
sponsble for the invoices management; then by sharing
the same resources for the payment authorization (in or-
der to keep to a fixed value the global amount of staff re-
source “Tot Res = 13”). In such way, we got a delay time
Table 4. Trend of the payment times given the value of
X.miss = 50% for different values of N. inv and N. Paym.
(day) N. inv N. paym Tot Res
112 4 4 8
100 5 4 9
87 6 4 10
76 7 4 11
67 8 4 12
66 9 4 13
43 8 + 1 4 + 1 13
33 7 + 2 4 + 2 13
32 6 + 3 4 + 3 13
for payments equal to just 32 days that would be abso-
lutely satisfactory for normal use.
Of course, all these results are just an indicatio n about
how the payment delay are related to the resource amount
and do not take into accoun t any additional delays due to
the relationships with banks or with the regional admini-
stration. The simulation values emerging from the simu-
lation are however consistent with the data coming from
the field experiences.
The Regional Centralized Agency guarantees significant
savings in health service and goods purchasing. The sup-
ply chain management requires a specific ICT based or-
ganisation and workflows. Becau se of the sharing of sup-
ply chain responsibility between the Regional Agency
and Health Companies, there are some critical issues that
have to be managed.
A strict level of automation and integration with the
PHC is required, in order to guarantee a real-time trans-
fer of accounting documents, as well as a perfect align-
ment of accounts in order to avoid inconsistencies be-
tween order/invoice/shipping documents/invoices that
would have serious rebound on the invoices’ settlement.
A workflow model representing some characteristic be-
haviours of a Regional Agency workflow is suggested: in
particular it allows to analyze the performance of the
system according to some critical features of this type of
Agency. The model simulation shows how important is a
correct management of the logistic related to the goods
delivery in order to ensure a timeline data entry of the
shipping documents in the information system; in fact,
the payment delay due to a feckless shipping documents
management (X.miss 50%), resulted unacceptable.
Therefore the management of a Regional Agency re-
Copyright © 2012 SciRes. IIM
A. PEPINO ET AL.
Copyright © 2012 SciRes. IIM
quires a strong control over PHC, which has the respon-
sibility of both the receipt and the verification of the de-
livery goods’ conformity. Given an average amount of
delayed shipping document (X.miss = 50%) and given a
productivity approximately around 800 invoices per
month for each personnel unit, (including invoices and
payment management) it would be possible, with ap-
proximately 13 personnel units, (where at least 9 of them
have to be shared between “invoice registration” and
“payment authorization” role), to manage a flow of about
200,000 invoices/years, guaranteeing an average time for
the accounting flow equal to about 30 days.
Although many information related to this model’s
structure have been derived from the field experience this
model could be used also for other similar case studies
Unfortunately some factors having a certain degree of
randomness, should be taken into account for example:
The presence of electronic invoicing flows (that, be-
cause of national policies costraints, must be consid-
ered residual respect to the ordinary invoice flo ws ).
Other automatism and specific aspects of the man-
The Personnel turn-over with relative training as-
In conclusion, a regional purchasing agency also playing
the role of payment central, because determines an addi-
tional level in the supply chain management requires
much attention about logistics and the conformity verifi-
cation of received goods, management, by PHC, who are
the final recipients of those provisions and responsible
for that. The logistic weakness by PHC resulted in more
staff necessity for the Regional Agency in order to guar-
antee the appropriate document management. By using
the proposed model it some general assessments could be
done: about the balance between the shipping document,
dispersion index, and the amount of additional adminis-
trative staff to be employed in The Regional Agency staff
to manage the documental flow. In other words, starting
from the document flow size, and the X.miss index it is
possible to determine the personnel quantity that is nec-
essary to guarantee the requested payment delay.
This work was supported in part by the scholarships for
the Ph.D. project in “Economics and Management of
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