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ORIGINAL ARTICLE
A synergetic mechanism for digital library service in mobileand cloud computing environment
Junsheng Zhang • Yunchuan Sun • Lijun Zhu •
Xiaodong Qiao
Received: 19 February 2014 / Accepted: 29 April 2014 / Published online: 19 August 2014
� Springer-Verlag London 2014
Abstract Digital library services in the mobile comput-
ing have come into our daily life with the development of
wireless communication and the manufacture of mobile
devices. Digital libraries have collected large-scaled data
for providing information service. However, there are still
many problems such as limitations of computing on mobile
devices and data transmission problems in the wireless
network. This paper proposes a synergetic mechanism for
digital library to provide information service in the mobile
and cloud computing environment, which combines the
digital library servers, mobile hosts and personal cloud
space into a synergetic work group seamlessly. The pro-
posed mechanism integrates the strong computing and
large-scaled storage ability of cloud computing together
with the convenience of mobile computing. It could help
promoting knowledge sharing and improve work efficiency
of users in the mobile and cloud computing environment.
Keywords Digital library services � Cloud computing �Mobile computing � Synergetic
1 Introduction
Accessing information and knowledge on the mobile
devices with wireless communication such as WLAN and
WiFi has become popular in recent years. At the same time,
digital libraries have become the most important knowl-
edge sources in the Internet era, especially for science and
technology research. Mobile and wireless communication
has been a part of our daily life with the development of
technologies such as wireless communication and the
integrated manufacturing of mobile devices. How to
acquire knowledge from the online digital libraries on the
mobile devices is now relevant to all the users that acquire
information and knowledge through the Internet for work
and amusement.
Internet has changed the way of information and
knowledge communication among people. Correspond-
ingly, it has influenced the information service style of
libraries. After the digital libraries occur, the number of
readers that go to the traditional library has been decreas-
ing. Libraries are becoming the combination of the tradi-
tional libraries and the digital libraries. Compared with the
traditional libraries, digital libraries could provide online
information services and promote the knowledge sharing
among people [5] more quickly and conveniently. With the
development of the Internet construction, more and more
information resources can be acquired from the online
digital libraries. The digital libraries store and provide
information and knowledge to people via the Internet.
Digital libraries are associated with large-scaled static
information repositories. Many large digital libraries such
as national libraries and data centers have been built for the
long-term information preservation. Portal websites like
Yahoo! and search engines like Google could be also
regarded as the special ‘‘large’’ digital libraries. The
J. Zhang � L. Zhu � X. Qiao
IT Support Center, Institute of Scientific and Technical
Information of China, Beijing 100038, China
e-mail: [email protected]
L. Zhu
e-mail: [email protected]
X. Qiao
e-mail: [email protected]
Y. Sun (&)
Business School, Beijing Normal University, Beijing 100875,
China
e-mail: [email protected]
123
Pers Ubiquit Comput (2014) 18:1845–1854
DOI 10.1007/s00779-014-0798-8
‘‘large’’ of digital libraries means that the size of data is
very large, and the number of information users is very
large. Resources in these digital libraries have various
types of information resource such as text, image, audio
and video. Because of the plenty of information resources,
digital libraries often have a large number of users. It
becomes a hard task for the large number of users to access
large-scaled data in digital library and satisfy the diverse
and personal information needs. Generally, user informa-
tion needs for the digital libraries include searching for
literature, fast response of user query, and statistical
information or data mining results for users’ decision-
making.
To process the large-scaled data and provide informa-
tion service, digital libraries need large-scaled data storage
ability and high performance computing ability. The
independent high performance computing platform is
expensive; therefore, computer scientists and engineers try
to find the approach to integrating distributed cheap com-
puting resources for powerful computing ability. Grid
computing has become the hot research topic [3, 8] during
the past decades. Grid computing has been studied in the
scientific computing applications at first, while enterprises
also have the requirement of large-scaled data storage and
power computing. With the development of Grid Com-
puting technology and the accumulation of large-scaled
data in databases and the Web, cloud computing comes
with massive data storage and integrated high performance
computing. The large-scaled data storage and high per-
formance computing resources are urgently needed by the
digital libraries, so the digital library services will be more
closely related to cloud computing [10, 19].
Large-scaled data flow between the digital library and
the users demands a larger width of the Internet. Queries
submitted to the digital libraries are complex because of
the diversity of user information needs. The literature may
belong to several research fields and can be used by
researchers from different research domains. Because the
purposes are different, different users may use different
queries for the same literature. Interactions between digital
library and users involve information preprocessing,
searching, navigation and presentation of distributed het-
erogeneous repositories of data. Usually, these interactions
need better Internet connections with high stability and
larger bandwidth. The bandwidth of the Internet for
information transmission has been continuously increasing,
which has enabled digital library services with large-scaled
data transmission.
Current data transmission on the Internet has two types:
wired communication and wireless communication. The
wired communication can provide stable and larger band-
width comparing with the wireless communication. How-
ever, with the development of wireless communication
technology and the continuous construction of mobile base
stations, the wireless communication has extended to a
large scope and merged with the Internet more closely.
Wireless communication has provided great conveniences
for our work and life. The wireless communication has
many merits such as mobility, convenience and wide ser-
vice scope comparing with the wired communication.
However, the shortcomings of the wireless communication
are also obvious, that is, small bandwidth, frequent dis-
connections, high bandwidth variability, predictable dis-
connections and monetarily expensive.
Mobile computing paradigm has emerged due to the
advances in wireless or cellular networking technology.
Mobile communication needs no wired connection to the
Internet. Mobile devices have to change their base stations
from time to time for the changes of places. Mobile hosts
such as smart phones (e.g. iPhone) and tablet PC (e.g. iPad)
make it convenient for users to connect with the digital
libraries in the mobile computing environment; however,
they still have natural shortcomings such as frequent dis-
connections, limited computing power, memory, and
screen size [3].
The mobile devices have been providing great conve-
nience for the moving people to access information. Many
people have to move between different places for work and
business, and they often need to access information via
mobile communication during their moving. In science and
technology research, researchers often move between dif-
ferent places for communications and cooperations. They
often need to search and acquire information from digital
libraries and search engines frequently. So how to provide
better digital library services in the mobile computing has
become more important for promoting the development of
research. However, the digital library services in the
mobile computing environment have many limitations.
Current mobile hosts connected to the digital libraries still
have the following problems:
• Frequently disconnections Although more base stations
of wireless communication have been built, the
disconnections still frequently occur because of the
weakness of signals caused by the structure and
material of buildings. The data transmission time
should be as short as possible, because the disconnec-
tions would lead to the retransmission of data and it will
increase the cost of data transmission.
• Band width is still narrow Comparing with the wired
communication environment, the wireless connection
has a lower width, so the large-scaled data transmission
is impossible in the low bandwidth communication
network. With the increase of Internet users, the speed
of information production is also very high, while more
users need more data transmission from the digital
1846 Pers Ubiquit Comput (2014) 18:1845–1854
123
library. This has formulated great pressure on the
bandwidth of communication.
• Memory and storage is limited The storage ability of
mobile hosts has been increasing, while the data size of
information are also changing with relatively higher
speed. And people find that the storage spaces of their
mobile devices are often full and they have to delete
some files from time to time to store the new data.
• Screen size is small The mobile devices are designed to
be convenient for carrying, so most of them are
designed with small screens. Small screens need the
information to be short and then large-scaled data are
split into more little-sized files or segments. In the real
applications, images and multimedia could be dis-
played on the small screen with low resolution while
the text could be displayed with summary.
• The input and interaction on mobile devices are still not
convenient comparing with the static hosts with
keyboard and mouse The touch and scroll of fingers
on the small screen should be as simple as possible. The
speed of data input is still very limited. So the mobile
devices always replace the input textbox with the
option selection buttons. Speech recognition technol-
ogy has been applied in the mobile devices for a more
convenient input, however, the precision still need to be
improved to suit the diverse and multilingual language
environment.
So the difficulties of digital library services in the
mobile computing can be classified into two types: the
shortcomings of wireless network and the shortcomings of
the mobile devices. To improve the digital library services
in the mobile computing environment, these following
shortcomings are limitations that cannot be avoided.
• The low band width and frequent disconnections are
two intrinsic shortcomings of wireless network. In the
current stage, possible solutions are as follows: one is to
compress the size of data, the other is to support the
discontinuous transmission on the Internet.
• The shortcomings of mobile devices need the novel
human–computer interactive approach that can input
information in a convenient and simple approach or
even no input [1].
The main information services of digital libraries
include query, recommendation and download. Query can
submit short text to the stationary hosts, especially the
digital library servers. Recommendation pushes the
potential useful information to the users without query
submission. Download will transmit the digital literature to
users via the Internet.
To improve the digital library services in the mobile
computing, the following can be done:
• Precise recommendation According to user’s profile,
relevant information can be recommended to the users.
• Offline computing and information push After the user
sends the query command to information provider,
digital libraries will compute and send result back to
users. If a user is not online, it should send the result to
an online space such as user’s Email or personal cloud
space.
This paper proposes a synergetic digital library service
mechanism in the cloud computing and mobile computing
environment. The mechanism could make the digital
libraries, mobile hosts and clouds work collaboratively.
2 Related work
Mobile agent is an important part in the mobile computing
system. A mobile-agent system, named Agent Tcl, is
described including the design and implementation. It
supports the mobile computers and disconnected operation
[9]. Its features include network-sensing tools and a
docking system that allows an agent to transparently move
between mobile computers, regardless of whether it is
connected to the network.
Ref. [11] surveys the fundamental research challenges
particular to mobile database computing, reviews some of
the proposed solutions and identifies some of the upcoming
research challenges. The authors give the interesting
research areas, including mobile location data manage-
ment, transaction processing and broadcasting, cache
management and replication and query processing. They
highlight new upcoming research directions in mobile
digital library, mobile data warehousing, mobile workflow
and mobile web and e-commerce.
Data management in the mobile computing is the key of
applications in the mobile computing. Ref. [2] surveys the
research problems in mobile computing and databases. As
the authors mentioned, mobile computing is a fertile area
of work for researchers in the areas of database and data
management. The inherent limitations of mobile comput-
ing systems present a challenge to the traditional problems
of database management.
Cloud computing has changed the means of service and
data storage of the applications. Cloud computing heralds a
new era of computing where application services are pro-
vided through the Internet. Cloud computing can enhance
the computing capability of mobile systems. Cloud com-
puting has been regarded as the ultimate solution for
extending battery lifetimes of mobile systems [10].
Challenges for mobile data management in the era of
cloud and social computing have been discussed [4]. There
is a trend for the occurrence of a new generation of mobile
Pers Ubiquit Comput (2014) 18:1845–1854 1847
123
data management solutions needed for the convergence of
mobile, cloud and social computing.
The digital resources could be preserved in the open
cloud [6]. This can be referred for the digital libraries to
provide information service. Digital library provides the
information of publications while the cloud space provides
the information storage for users.
Mobile devices like a smart phone have become one of
main information processing devices for users. Users with
smart phones can not only answer and make calls, but also
execute some information processing tasks. However,
a mobile device is still resource constrained, because
some applications usually need more resources than a
mobile device can afford. So a mobile device should get
resources from an external source. One of the possible
sources is the cloud computing platform. Nevertheless, an
access to these platforms is not always guaranteed to be
available and/or is too expensive to be accessed. The
authors envisioned a way to overcome the issue by cre-
ating a virtual cloud computing platform using mobile
phones. Due to the pervasiveness of mobile phones and
the enhancement in their capabilities, the idea is feasible
[7].
Human computer interaction plays an important role in
the mobile systems. Ref. [12] presents an overview of
human computer interaction (HCI) issues in mobile sys-
tems based on publications from 1998 to 2002. The
research has been summarized in two taxonomies, one by
research topic and one by design lifecycle stage. These
taxonomies highlight the areas where most research was
focused and the areas that are lacking research.
Current digital library information services in the mobile
computing include the following styles: one is short mes-
sage service (SMS)-based information service and the other
is wireless application protocol (WAP)-based information
service [15]. SMS-based information service provides
information after editing the user needed information, so it
is very hard to provide the on demand query. WAP-based
information service provides less information because the
resources are not so many.
In the cloud computing environment, the semantic
links among different users and their information can help
to improve the information service [16]. The downloaded
information resources have some relationships such as
sameAuthor, sameTopic, citation, before and after. The
semantic relationships connect information resources into
a semantic link network, which implies the interests of
users. Events extracted from big data can be further
weaved into semantically linked networks, namely event-
linked network (ELN), through semantic links among
events [17]. ELN model can also been used to organize
the big sensing data in the Internet of Things efficiently
[18].
3 Our approach
3.1 Query types
According to the response time of digital library servers for
processing the query, information requirements from
mobile hosts can be classified as follows:
• Real-time query For example, user wants to know the
latest literature about a research topic or search a
specific literature that the user knows the title, publi-
cation venue and author information definitely. In the
real-time query, user wants to know the result imme-
diately, so the digital library servers should process the
query quickly and provide the precise and brief answers
to users in a short time. The information should be
browsed conveniently on the mobile devices.
• Delayed query For example, users want to download
what they need or know the query result after a longer
time or even the reconnection with the digital library
server or their personal cloud space. The processing and
response of digital library server is not very urgent, so
the digital library servers have more time to process the
query and provide the literature or return result to the
agent (private cloud space or user Email) when mobile
host is off-line.
The processing methods for different queries are also
different. The real-time query is processed immediately by
the digital library server and the short answer information
is returned to the mobile host. Tasks that need long time
such as download, recommendation and news broadcast of
digital library are transferred to the personal cloud space or
user’s email in the delayed query style. According to the
different requirements of response time, the digital library
servers could assign the information service queue and
finish the query tasks efficiently.
Because the screen size of the mobile hosts is small and
the input of query is not convenient, the query should be as
short as possible or even no query. Short query is often the
words or phrases relevant to metadata of information
resources such as title, author, keywords and subjects or
keywords from the full text. If the digital library knows the
user information need, it can recommend information to
the user without query input. No-query information service
is based on the information recommendation or user’s
subscription and history information of the historical
download information.
Because the bandwidth of mobile network is low and the
communication are often disconnected, the query result
should be short, and the query results are often based on the
metadata, while the full text download is often in the
delayed query style. The query result and recommendation
computing can be executed on the servers of digital
1848 Pers Ubiquit Comput (2014) 18:1845–1854
123
libraries with large storage ability and high performance
computing ability. The mobile hosts are only used to
receive the query results.
To overcome the limitations of mobile communication,
cache in the digital library server side and prefetch in
mobile host side could improve the information service
quality. The frequently submitted queries can be cached on
the servers of digital libraries, which can provide the
cached result to users directly for the quick response.
Because the bandwidth of mobile network is low, mobile
host can prefetch the relevant data and information when
user is browsing. Prefetch strategy can be based on the
semantic links between the contents that user is browsing
and the information mostly possibly to be downloaded by
mobile users [14]. The prefetch strategy can improve the
browsing experience on the mobile host with less waiting
time for download. However, the prefetch strategy will
increase the cost of data transmission if the prefetched data
are not interesting for the users.
3.2 Synergetic mechanism design
To satisfy the information requirements of users, it is
necessary to build a synergetic mechanism containing the
digital library, mobile host and cloud space.
Figure 1 shows the synergetic mechanism of digital library
service in the cloud and mobile computing environment.
Digital library servers, mobile hosts and personal cloud spaces
together formulate the digital library information service
system in the cloud and mobile computing environment.
Stationary hosts can also take part in the digital library
information services, by submitting query to digital library
servers and synchronizing with the mobile hosts.
The combination of stationary hosts and the mobile
hosts could make the users work more conveniently, and
the key technology is the synchronization among the sta-
tionary hosts, personal cloud space and the mobile hosts.
During the synchronization, the personal cloud space can
act as the bridge between stationary hosts and mobile hosts.
Because the personal cloud space is always online, the
users can access their information resources from their
stationary hosts or mobile host with wired or wireless
internet connections.
As Fig. 1 shows, the synergetic mechanism of digital
library services contains the following parts:
1. Digital library server The digital library server part
may contain one or more digital library servers. This
part stores the literature resources, processes the query
and provides historical download log service and
recommendation service. Digital library server part is
the provider of information resources and information
services.
2. Cloud service provider The cloud computing service
provider stores the user downloaded information
resources and provide user’s profile information to
the digital library server. The cloud computing service
provider acts as the agent between the digital library
server and the mobile host. It can work continuously
whether the mobile host is online or offline. Cloud
service provider ensures the information access for
users if they can access the Internet via a stationary/
mobile host.
3. Mobile host Mobile host submits queries and subscrip-
tions to digital library server and then receives
information from the digital library server or access
the data in the personal cloud space. The mobile host is
Digital Library Servers
UserAuthentication
Personal Cloud Space
Mobile Host
Stationary Host
Submit Query/Command
Return Short Result
Submit Query/User Command
Return Result
Data TransferUser Profile
Mobile Connection
Wired Connection
Synchronization1
2
3
4
Fig. 1 The synergetic
mechanism of digital library
service in the cloud and mobile
computing environment. Solid
arrows mean data transmission;
dotted arrows mean the data
transfer in wired Internet
connections; and, the dotted
lines mean the user
authentications which are
associated with the digital
library servers, personal cloud
space and mobile hosts during
the digital library services
Pers Ubiquit Comput (2014) 18:1845–1854 1849
123
the information consumer and the synergetic digital
library service initiator. Because the mobile hosts are
carried by the users, they are the customers of
information services. Most information services are
initiated by the users, so the mobile hosts are the
initiator in the synergetic mechanism.
4. User authentication is important to ensure the security
and privacy and it is relevant to all the three parts in
the synergetic mechanism. Authentications for infor-
mation access are checked on the digital library server,
personal cloud space and mobile host.
• Authentication in the digital library server part
enables the accesses from stationary/mobile hosts
and cloud spaces.
• Authentication in the personal cloud space part
enables the data transmission from digital library
server to the personal cloud space, and from the
personal cloud space to mobile host or the station-
ary hosts with wired connections.
• Authentication in the mobile host enables the
authenticated user to connect with digital library
server and the personal cloud space.
In the synergetic mechanism, the authentication
accounts in different parts should be consistent, that is, the
same user name and password.
Based on the synergetic mechanism, the information
service styles can be classified into two types: passive
information service and active information service.
• Passive information service A typical digital library
information service in the mobile computing environ-
ment is as follows:
1. User sends a query to the digital library server with
mobile host via the wireless network.
2. Digital library server processes the query and sends
the answer information back to the user. During the
processing of query, the digital library may connect
the user’s personal cloud space (if configured) to
acquire the user’s profile for more precise and
personal information search.
3. User makes the decision and sends a command
such as ‘‘download’’ or resubmit a new query to the
digital library server.
4. Digital library server receives the user command,
executes it, and then sends the execution result
back to the mobile host or the personal cloud space
according to the user’s option. Users can know the
service result via the mobile host or connecting to
the personal cloud space.
• Active information service The digital library server can
process the user’s query personally based on user’s
profile. To build the user profile, there are two possible
ways: one way is to provide the interest form for the
user to fill and submit, the other is to analyze the user’s
interests according to the historical data of the user’s
query and downloaded information. The former way
can be provided by users, while the latter way will use
the text mining technology. The processes of text
mining can be executed in the personal cloud space,
and it can update the user’s profile in time. After the
user has interactions with the digital library server, the
historical data of interaction data can be used to analyze
and mine the user’s interests by using data mining
techniques [20].
3.3 Merits
Compared with the traditional digital library service, the
merits of the proposed synergetic mechanism are as
follows:
1. It can work continuously with less limitation of Internet
connection The digital library servers can provide the
required information to the cloud space of the users if
the mobile host is offline. In the traditional style, the
download of information should be under the condition
that the mobile host and the digital library server are
connected, and the information transmission will be
terminated automatically if the Internet connection is
stopped. In our synergetic mechanism, the information
transfer can be executed according to the user’s
command sent from the mobile host. The information
service can be provided even the mobile host is offline
after the information need is sent to the digital library
server. The cloud service can be always online, so the
cloud service can be regarded as a no-resting agent
between the digital library and mobile host. When the
command of the user is executed, the agent in the
digital library server side can report the result to the
mobile host immediately via short message notification
or when the mobile host is reconnected with the digital
library or their personal cloud space. The notification
approach can be chosen by users.
2. More information can be accessed through the cloud
space with less limitation of the storage of mobile
devices Cloud computing service can provide more
storage space and computing power to user, and it also
saves the time and cost of communication from the
mobile host. Besides, the historical download log data
in the cloud space could be used to analyze the profile
of users including the user’s interests and possible
information requirements. The historical information
could help to recommend the right information to the
1850 Pers Ubiquit Comput (2014) 18:1845–1854
123
right users in the right time, which is the ultimate aim
of the knowledge management and knowledge service.
Cloud computing service provider stores the informa-
tion that the user needs, and the user can access these
data when (s)he is connected with the mobile host or
other stationary hosts with wired internet connections.
This merit is mainly carried by the cloud computing
environment.
3. User’s work places could be wider with the mobile
communication The mobile host connects the user, the
digital library and the cloud space at places that wireless
communication service covers. Mobile hosts could transfer
the user query and command to the digital library servers
through the mobile and wireless communication. The user
query and command sent by user are often short, which is
suitable for the mobile communication. The tasks that need
more computing time, larger storage space, and more
internet transfer can be done by interactions between the
digital library servers and the personal cloud space in the
cloud computing environment. This merit is mainly carried
by the mobile computing environment.
In summary, the synergetic mechanism has combined the
merits of cloud computing (such as large storage and online
characteristics) and the merits of mobile computing (such
as the mobile and wide signal coverage) for enhancing the
digital library information services and making the users’
work conveniently and continuously.
4 Data management
To implement the proposed synergetic mechanism of dig-
ital library service in the cloud and mobile computing
environment, data management is an important task.
Figure 2 shows the data management in the digital library
information service based on the proposed synergetic
mechanism. The data management in the synergetic mech-
anism contains three parts: data in the digital library, data in
the cloud space and data in the mobile/stationary host.
4.1 Data in the digital library
The data size in the digital library is very large. All the
data in the digital library information service are related to
the data in digital libraries. The data in digital library
includes: the data of information resources (such as raw
data and metadata) and the user data (such as user profile
and their historical query data).
• Raw data the raw data are the digital information
resources, which may be text, image, audio and video
etc. The raw data contain the detailed information, and
they are stored in the digital library servers. If users
choose to download them, the chosen raw data will be
transferred to user’s stationary/mobile host or the
private cloud space of users.
• Metadata metadata are the descriptive information of
information resources such as title, author, publication
venue, research institute, publishing time and publisher
of the specific literature. The metadata can help user to
understand and identify the content of the information
resources. The metadata are often used to search
information resources that users need.
• Cache data because the digital library often receives
similar information needs, the frequent query result can
be cached on the digital library server side to shorten
the response time of information service. The cache
data will be changing according to the time, because the
topics of the queries are often changing. When the size
of cache data is too large, it is necessary to be cleaned
frequently.
• Historical data during the digital library information
service, the historical data are recorded as service log in
the digital library servers for all users, personal cloud
space and the mobile host for personal users. Historical
data on the digital library server and personal cloud
space can be used to mine and discover the user profile,
while the historical data on mobile host can be used to
speed up the duplicate query and downloaded informa-
tion access such as browsing if the cache data in the
mobile host are not cleaned.
Wired/wireless Network
Information ConsumerStationary/Mobile Host
Prefetch Data
Query Data
Download Data
Raw Data
Metadata
Cache Data Historical Data
Information ProviderDigital Library Server
Personal Cloud
Query Answer
Authentication Data
(Public Access) Cloud
Fig. 2 Data storage in the synergetic mechanism for the digital
library information services: information provider such as digital
library servers stores the raw data, metadata, cache data and historical
data; information consumer such as stationary host and mobile host
stores the user data including the historical download data, query data
and prefetched data; cloud space provider provides the storage space
of private cloud and the authentication data which is accessible for
public to serve the authentication check
Pers Ubiquit Comput (2014) 18:1845–1854 1851
123
4.2 Data in stationary host or mobile host
During the information service between digital library and
users, data in the stationary host or mobile host are close to
users. These data are query data submitted by users,
download data by users and prefeteched data by stationary/
mobile hosts.
• Query data query submitted to the digital library can be
classified into two types, that is, on demand and
broadcast. Correspondingly, the data for query service
can be classified into on demand data and the broadcast
data. On demand query can process the information
requirement of users by using the query or subscription
in the one-to-one mode, while in the broadcast type
service, the digital library servers can publish the new
changes of information resources for users to choose in
the one-to-many mode.
• Download data when the user find interesting informa-
tion resources, (s)he often downloads them to their
stationary/mobile host or the personal cloud space. So the
downloaded information resources will imply the user’s
interests. After the information resources are down-
loaded, the usage information also implies user’s inter-
ests and the possible user information needs in the future.
• Prefetched data during the online reading or browsing,
user can choose to prefetch data on the mobile host to
improve the fluency of information browsing on the
mobile host. The caching and prefetch approach can
improve the information service quality and the user
experience. However, the prefetech strategy may
increase the cost of data transmission if the downloaded
data are not needed by users.
4.3 Data in the cloud
As cloud service provider acts as the agent between the
digital library servers and the mobile hosts, the data in the
cloud are more than the data in the mobile hosts. If the
storage space of the mobile host is large enough, data in the
mobile host could have been equal to the data in the cloud
space. The user can choose the subset of data in the cloud
space for synchronization with the mobile hosts. With
different synchronization strategy, the data in the cloud
space will increase and record the usage of information
resources in digital library by the users. The historical data
reflect the changes of the users. Besides of the users
download information resources, authentication data can
also be stored in the cloud space for ensuring the privilege
of information access between digital library servers,
mobile hosts and personal cloud spaces.
• Authentication data are often stored and maintained by
the public cloud providers such as Google. Users can
access the digital library servers and their personal
cloud space by using their Google accounts which are
often shown as the Gmail account. A Google account
could be used as the general account to access different
web applications, and this could avoid too many
registrations for different web-based applications.
• Personal data in the personal cloud space include the
query data, download data and historical data, which
are often synchronized between personal cloud space
and stationary/mobile host. Personal data can be open
to others according to the settings of users for
information resources.
5 Discussion
During the implementation of the proposed synergetic
mechanism, the cloud space provider can be combined with
the digital library servers or replaced by other storage space
providers. So the proposed synergetic mechanism is also
suitable for the scenarios that the communication envi-
ronment has no cloud computing but only the mobile
computing.
• The roles of digital library server and the personal
cloud space can be combined. Digital library server part
and cloud computing service provider part can be
combined into one part, that is, the digital library server
acts as the cloud service provider at the same time. If
the digital library server and the cloud computing
service provider are combined, the data storage and
download information storage can be integrated. The
cloud space only records the URL of information
resources that user downloaded, and this will reduce the
storage space.
• The personal cloud space provider can be replaced by
the traditional storage space provider such as net-drive
and even the user’s Email box. If the mobile host sends
the command to the digital library to transfer the
information to an Email box or a net-drive space, the
data transfer can be executed, and users can connect
their emails or net-drive to acquire their data.
The synergetic mechanism is extensible for stationary hosts
to acquire information from the digital library servers.
Although the mechanism is designed for the mobile com-
puting environment, it is also applicable to the wired
connection environment. Users can query and send the
download command to digital library server with the
mobile hosts, but when the data are transferred to the
personal cloud spaces, all the data can be accessed either
from the mobile host or the stationary computers through
1852 Pers Ubiquit Comput (2014) 18:1845–1854
123
wired connections. Furthermore, the data can be synchro-
nized between the mobile host and the stationary host.
Then users can access data through both the wired and
wireless connections seamlessly.
Users can continue their work on a stationary host with
wired connections. In the synergetic mechanism, the data
can be accessed from the digital library server or cloud
space. The data receiver host can be mobile devices or the
stationary computers. With the user authentication check
on digital library servers, mobile/stationary hosts and per-
sonal cloud spaces, the data transferring becomes syner-
getic, and the synergetic digital library service mechanism
can help the users to access data and knowledge in digital
libraries more conveniently.
During the implementation, there are some factors to be
focused on: user interface design, security and privacy
protection.
• User Interface design The limitations of mobile host
such as inconvenient input and small size screen have
decided that the GUI design on the mobile host is quite
different from the stationary hosts such as personal
computers and laptops. The GUI of digital library
service for the mobile host should be simple and needs
less or even no input design. Generally, the mobile
devices need the automatic text summary to display the
useful information on the small screens.
• Security and privacy Security and privacy are important in
any information management system. The security in the
cloud computing has been discussed in [13]. In the
synergetic mechanism, the mobile host, digital library
server and cloud service should execute the authentication
check for users. The security of authentication data in the
synergetic mechanism is decided by the privacy protection
from the cloud service providers. However, in the current
web-based applications, users have to login different
websites with different account to ensure the authentica-
tion of users in order to access the information resources.
When the authentication is unified, the users can access the
same account to visit different applications.
After the synergetic mechanism for digital library infor-
mation services is implemented, there are many possible
applications, especially, supporting the information
resource acquirement in the mobile environment.
Before a decision is made, the necessary literature
should be prepared for the survey. When a user is in the
journey, (s)he could use mobile devices like smart phones
to connect to the digital library servers and the personal
cloud space. If (s)he finds the proper information, (s)he
could collect the literature into the personal cloud space
and then read these literatures with the computer or mobile
devices with good Internet connections. This approach can
make the user work more efficiently. Besides, when a user
is working but (s)he has to leave for another place because
of another urgent task while (s)he is right in the middle of
the work. Then, (s)he could tell the digital library server to
execute the current task continuously and send the infor-
mation resources to the personal cloud space. After the
command is sent, the stationary/mobile host could be off-
line, while the information acquirement task will be exe-
cuted without interruption. The user can monitor the
execution of the task by using the mobile devices when
(s)he is moving and receives the service result reported by
the agent(s) in digital library server or the personal cloud
space. In this process, the mobile host acts as the com-
mander, while the digital library server and the personal
cloud space could work continuously according to the
command from the mobile host.
The synergetic mechanism for digital library services
makes it more convenient for users to access information
resources from the digital libraries by using the mobile
wireless communication. The mechanism will ensure the
continuous work without disturbing from the Internet dis-
connections because of location change. Especially, it is
efficient to finish the information preparations such as
query and download for the work, compared with the
previous digital library service which is carried on only in
the wired Internet environment. The web applications and
portals for the mobile devices will be a prosperous research
field for promoting the digital information sharing.
6 Conclusion
Digital library services in the mobile computing environ-
ment have come into our daily life because of the develop-
ment of wireless communication and the manufacture of
mobile devices. However, the digital library services with
large-scaled data are not very suitable for the mobile devices
and wireless communication. In this paper, we propose a
synergetic mechanism for digital library services in the cloud
and mobile computing environment. It combines the digital
library servers, mobile hosts and personal cloud space into a
synergetic work group seamlessly. The proposed mechanism
can help promoting the knowledge sharing and improve the
work efficiency by speeding up the information transferring
between digital library and users by decreasing the influ-
ences of limitations of little storage space and data trans-
ferring under the Internet connections.
Acknowledgments This research work was partially supported by
International Science & Technology Cooperation Program of China
under grant No. 2014DFA11350, ISTIC research foundation projects
XK2014-6; and, National Natural Science of China (Grant
No.61371185 and 61171014).
Pers Ubiquit Comput (2014) 18:1845–1854 1853
123
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