Int. J. Communications, Network and System Sciences, 2010, 3, 877-887
doi:10.4236/ijcns.2010.311119 Published Online November 2010 (
Copyright © 2010 SciRes. IJCNS
Web Service Generation through Program Slicing*
Yingzhou Zhang1,2,3, Wei Fu1,3, Geng Yang1,2, Lei Chen1,2, Weifeng Zhang1
1College of Computer, Nanjing University of Posts and Telecommunications, Nanjing, China
2State key Lab. of Networking & Switching Technology, Beijing University of Posts & Telecommunications, Beijing, China
3State Key Lab. of Novel Software Technology, Nanjing University, Nanjing, China
Received August 21, 2010; revised September 25, 2010; accepted October 26, 2010
As the development of web service (WS), applications based on web services (WS), which are convenient
and platform-independent, have become increasingly popular in recent years. However, how to identify,
generate and compose services are still open issues. This paper proposes a method based on program slicing
to realize the generation and composition of web services. This paper introduces the method about how to
generate a WSDL file and a SOAP message from source codes as well as the theory of function dependence
graph (FDG). In addition, this paper gives an approach to generate a proxy service for each service, which
allows users to easily call a service. The results of experiments show that our generation and composition
methods of WS are feasible and flexible.
Keywords: Web Service, Arogram Slicing, WS Generation, Function Dependence Graph, Haskell
1. Background and Related Work
1.1. Program Slicing
Mark Weiser [1] first defines a program slice S as a re-
duced executable program obtained from a program P by
removing statements, such that S replicates part of the
behaviour of P. In general, a program slice consists of
those statements of a program that may directly or indi-
rectly affect the variables computed at a given program
point. The program point p and the variable set V, de-
noted by <p, V>, is called a slicing criterion. For exam-
ple, Figure 1 gives the slicing results for some interest
variables of source codes.
Program slicing algorithms can be roughly classified
as static slicing and dynamic slicing methods, according
to whether they only use statically available information
or compute those statements that influence the value of a
variable occurrence for a specific program input [2-4].
Program slicing can also be divided into forward slicing
and backward slicing [5,6]. In forward slicing, one is
interested in what depends on or is affected by the entity
selected as the slicing criterion. In backward slicing, one
is interested in what affects the variables in the slicing
criterion. To help readers understand program slicing
more deeply, Figure 2 gives an example of forward and
backward slicing.
1 void EgForSlicing ( ) 1 void EgForSlicing ( )
2 { 2 {
3 int a = 0; 3 int a = 0;
4 int b = 0; 5 int c = 5;
5 int c = 5; 6 if (c > 10)
6 if (c > 10) 7 a ++;
7 a ++; 10 }
8 else (3) static slicing for <10, a>
9 b ++;
10 } 1 void EgForSlicing ( )
(1) source codes 2 {
4 int b = 0;
5 int c = 5;
1 void EgForSlicing ( ) 6 if (c > 10)
2 { 8 else
5 int c = 5; 9 b ++;
10 } 10 }
(2) static slicing for <10, c> (4) static slicing for <10, b>
*This work was supported in part by the National Natural Science Foun-
dation of China (60703086, 60873231, 60873049, 60973046), Jiangsu
atural Science Foundation of China (BK2009426), Qing Lan Project
of Jiangsu Province, Jiangsu Innovation Project for postgraduate culti-
vation (CX10B195Z).
Figure 1. Source co de s and slicing results.
878 Y. Z. ZHANG ET AL.
1 read (n); 1 read (n); 1
2 j : = 1; 2 j : = 1; 2
3 sum : = 0;
3 3 sum : = 0;
4 acc : = 1; 4 acc : = 1; 4
5 while j < = n do 5 while j < = n do 5
6 sum : = sum + 1; 6 6 sum : = sum + 1;
7 acc : = acc * j; 7 acc : = acc * j; 7
8 j : = j + 1; 8 j : = j + 1; 8
9 write (sum); 9 9 write (sum);
10 write (acc); 10 write (acc); 10
(a) source codes (b) backward slicing (c) forward slicing
for < 10, acc> for <3, sum>
Figure 2. Examples of forward slicing and backward slicing.
1.2. Web Service
According to the W3C group [7], a WS (also webservice)
is traditionally defined as a software system designed to
support interoperable machine-to-machine interaction
over a network. It has an interface described in a ma-
chine-processable format such as WSDL (web services
Description Language) [8,9]. Other systems interact with
the WS in a manner prescribed by its description using
SOAP (Simple Object Access Protocol) messages, typi-
cally conveyed through HTTP with an XML serialization
in conjunction with other web-related standards.
Web services today are frequently just application pro-
gramming interfaces (API) or web APIs that can be ac-
cessed over a network such as the Internet, and be executed
on a remote system hosting the requested services [10].
In general, a service depends on other services. Such
dependences can be described as dependence graphs on
which program slicing algorithms can be applied for WS
generation and composition. All of the algorithms ap-
peared in this paper are implemented in language Haskell
which will be introduced in next subsection.
1.3. Haskell
Haskell [11,12] is a lazy, pure functional programming
language. It is called lazy because expressions which are
not needed to determine the answer to a problem are not
Haskell is a functional language because the evalua-
tion of a program is equivalent to evaluating a function
in the pure mathematical sense [13-15]. This differs from
standard languages (such as C or Java) which evaluate a
sequence of statements.
In this paper, we choose Haskell as our implementa-
tion language for the reason that it is lazy and pure as it
is mentioned above. Haskell possesses an expressive
syntax and have rich built-in data types; it is good at
handling complex data and combining components. It
has lazy semantics: no expression is evaluated until its
result is needed. The laziness can encourage the combi-
natorial and dynamic design of web services. By using
Haskell, we can write more bug-free, readable and ex-
tensible codes in less time. In addition, Haskell has an
advantage of computing mathematical expressions, which
is also useful for us to develop WS tools.
1.4. Related Work
Many researchers are doing some related work about WS
generation and composition [16,17]. They give some
methods and models to solve the problem how to discover
and generate a WS. The most two common methods used
recently are based on syntax and semantics [18-20].
The method based on syntax is a traditional one. Al-
though this method has been improved by a large number
of researchers, it has a known shortcoming when it uses
the technology of keyword matching, which often returns
some inaccurate results. Many services discovered by this
method are not wanted for users.
The method based on semantics does a better job than
one which is based on syntax. Its results of discovering
services are more accurate. However, there is still a big
step to be made to put semantics web services into prac-
tical applications for semantics’ complex definitions.
Some researchers have studied on generating and
composing web services by using program slicing tech-
nology, but most of them focus on prepare work for web
services, and haven’t proposed a feasible method with
the whole process of WS generation and composition
[21-25]. Rodrigues and Barbosa [26] gave a method for
analyzing the relationship between all components in
Haskell types/codes. They use program slicing to gener-
ate sliced codes for Haskell components. However, they
Copyright © 2010 SciRes. IJCNS
make less statements in detail about the follow process of
WS generation, such as how to generation WSDL docu-
ments. What is more, as mentioned in Subsection 1.3,
Haskell types/functions are pure and lazy, so their meth-
ods of component discovery and function dependence
graph can’t directly be used for the imperative languages
such as C and Java. In this paper, we will make a de-
tailed method about how to generate and compose web
services from source codes. The technology of program
slicing is used to help us abstract function dependence
graph (FDG) and generate corresponding services. Our
current prototype of WS tool can cope with the impera-
tive languages C and Java, and the functional language
Haskell as well.
The biggest difference between our work and others’
is the services’ dependences are added when they are
generated and published. These dependences make the
result more accurate when we do WS discovery for the
reason that we can filter the result which is obtained by
the discovery through the method of keywords matching.
And another difference is that we use program slicing
and graph theory to process services’ dependences.
The theory of function dependence graph is to be dis-
cussed in Section 2, and services identification with pro-
gram slicing is to be introduced in Section 3. WS genera-
tion and composition will be introduced in Section 4. In
Section 5, conclusions are drawn and future work is listed.
2. Function Dependence Graph
Program slicing is always based on some dependence
graphs such as the control dependence graphs (CFG) and
the program dependence graphs (PDG) [26], whose basic
node is a statement fragment. However, in our work, func-
tion is the basic unit. This will help us to divide source
codes into many fragments/components for generating
sliced codes of web services. So this section will introduce
functional dependency and function dependence graph.
When parsing a source code, a FDG will be generated
to record dependences between functions. For simplicity,
a function dependence graph is a set, where each element
is noted as (a, b), which indicates that the function a de-
pends on the function b and is expressed by an arrow
from a to b, i.e., a b. For example, Figure 3 gives a
FDG of a source code. In Figure 3, each letter in the box
stands for one function.
When analyzing the FDG, we need to derivate new
elements by doing some operations to elements in the
FDG. * Operation is defined to derivate new dependency
through some exist dependency in a FDG.
Definition 1: * operation is the transitive relation op-
eration which obeys the following rules:
(a, b) * (b, c) = (a, c)
(a, b) * (d, c) = (ø, ø)
(a, b) * (ø, ø) = (a, b)
where a, b, c, d are arbitrary functions such that b d,
and ø indicates a non-existent function.
In general, the * operation obeys the combination law
as follows:
((a, b) * (b, c)) * (c, d) = (a, b) * ((b, c) * (c, d))
where a, b, c, d are arbitrary functions. However, * op-
eration does not always obey the commutative law.
For example, in Figure 3:
(x, y) * (y, g) * (g, h) = (x, h)
(x, y) * (g, h) * (y, g) = (ø, ø)
Therefore, (x, y) * (y, g) * (g, h) (x, y) * (g, h) * (y, g).
Based on the transition operation *, we introduce the
follows the direct dependence relation and the indirect
dependence relation. If a tuple (a, b) exists in a FDG, the
relationship between a and b is the Direct Dependence
Relation (DDR), i.e., b is the direct dependent function
of a. If a tuple (a, c) does not exist in a FDG, but it can
be computed through * operation of several tuples in the
FDG, the relationship between a and c is Indirect De-
pendence Relation (IDR), i.e. c is the indirect dependent
function of a.
For example, in Figure 3, (y, g), (g, h), (g, i) are
DDRs and (y, h), (y, i) are IDRs.
In order to apply some slicing methods on FDG for
generating web services from source codes, we give two
slicing operations. <Operation is the backward slicing
operation which begins at the node in a slicing criterion
and finds all DDRs recursively>. Operation is the for-
ward slicing operation which can be derived from <op-
eration>. Assuming that c is a slicing node and S is a set
of tuples, we have the following equation.
c > S = (c < ( S)
) (1)
Figure 3. A sample FDG.
Copyright © 2010 SciRes. IJCNS
880 Y. Z. ZHANG ET AL.
Where operation is inverse relation of a tuple set, i.e.
S = {(b, a) | (a, b) S} (2)
For example, in Figure 3, if y is chosen to be a slicing
node and the FDG is noted as S, the result of computa-
tion y < S = {(y, f), (y, g), (g, h), (g, i), (f, g), (f, k)}, and y
> S = {(x, y), (z, y)}.
3. Service Identification with Program
3.1. Slicing Process
When a server receives some source codes from users, its
important work is to identify components/services from
the source codes. Non-strictly speaking, each top-level
function (or a class in object-oriented languages such as
Java) in source codes can be abstracted as a compo-
nent/service. For simplicity, a global variable or a point
variable in C is treated as the special function whose
parameter and return are both itself.
For WS identification, source codes will be parsed to
build a FDG on which some slicing operations are ap-
plied, and then the sliced codes for each service can be
easily generated. The main functions of the slicing proc-
ess will be listed below before describing the algorithm
of slicing in details.
code begins:
codes readFile (file);
AST generateAST (codes);
FDG generateFDG (AST);
SN chooseSlicingNode (FDG);
FDG slicing (SN, FDG);
AST compare (FDG, AST);
slicedCodes writeCodes (AST)
code ends
Figure 4 shows the slicing process framework of WS
identification from source codes. The slicing process can
be divided into five steps below.
Step 1. Produce the abstract syntax tree (AST [26]) for
Figure 4. Program slicing framework for WS identification.
a source code.
For convenience, the data type Method is defined as
follows to record information about a function.
data Method = (Name, Paras, Return, Location, Method)
The Method type has five child types: Name, Paras,
Return, Location, Method, which records the current
method name, its parameters’ name and types, the return
type, the location information, and the other method type
in its DDRs of the functions respectively. The Method
type is a recursive type for the reason that a Method type
would exist in another Method type.
We will generate an instance of the Method type for
each function in source codes. After finishing parsing the
codes, many instances of the Method type can be gener-
Step 2. Generate a FDG from the AST of source codes.
A FDG is in fact a set of function tuples. FDG can be
generated as long as this set can be obtained from the
Method type. As mentioned above, the Method type is a
recursive type, so a recursive algorithm is descried into
two steps to process an instance of the Method type. The
first step is processing parent instance of the Method
type and the second step is processing the child instance
of the Method type of the parent instance.
Step 2.1: checking whether the value of child Method
in a parent Method is NULL. If the value is NULL, no
tuple will be generated, and if not, a tuple (Method.Name,
Method.Method.Name) will be generated.
Step 2.2: assigning parent Method’s value with child
Method’s value and implement Step 2.1 again.
The follows gives the corresponding function code of
processing an instance of a Method type.
tuple Method =
if (Method.Method == NULL)
then NULL;
else return (Method.Name, Method.Method.Name);
tuple Method.Method
A set of function tuples can be abstracted from AST
through processing all instances of the Method type.
Then, the FDG can show all function dependences of a
source code.
Step 3. Implement slicing on a FDG at a slicing node.
A simple way to fulfill this step is to implement <op-
eration and> operation on a FDG.
The algorithm of this step is also a recursive one and
divided into two steps. The first step is to find DDRs of a
slicing node and the second one is processing the DDRs
found in the first step.
Step 3.1: finding all direct dependent functions of a
slicing node.
Step 3.2: If the result functions in Step 3.1 is NULL,
the algorithm will come to an end. Otherwise, its direct
dependent function will be treated as a new slicing node
Copyright © 2010 SciRes. IJCNS
and Step 3.1 will be implemented again.
The corresponding function code of Step 3 is listed
slicing (SN, FDG) =
{ SN
getDirectDependence (SN, FDG);
if SN
== NULL then NULL;
else slicing (SN
, FDG) }
where SN is a slicing node.
In this paper, we focus on backward slicing because
the generation of sliced codes is based on the result of
implementing backward slicing from a slicing node. Af-
ter Step 3, a FDG will be generated.
Step 4. Pruning the AST of source codes according to
the FDG obtained in Step 3.
After Step 3, we can obtain all the names of the nodes
in the FDG. We then decide to remain or delete a
method name in AST according to whether or not it is in
the FDG. Its implementation function code can be found
compare (FDG, AST) =
{ nodes getAllNodes FDG
Method getASTMethod AST;
again: if (search (Method , nodes) == False )
then delete Method;
Method = Method
Goto again;
else remain Method;
Method = Method
Goto again }
Step 5. Generate sliced codes from source codes ac-
cording to the AST from Step 4.
The algorithm of this step is rather easy because the
location of a function in the source codes can be obtained
from the Method.Loacation type. The only work to do is
to abstract functions in the AST from source codes and
put them together into sliced codes.
Figures 5-7 below show the results of a slicing proc-
ess. With our WS toolkit prototype, Figure 5 shows the
sample C code in its left frame, whose FDG is shown in
Figure 6, and the sliced code for the function “fun3” in
its right frame, whose FDG is shown in Figure 7. As
mentioned at the beginning of this section, we treat a
global variable as a particular function whose parameter
and return are both itself. So, in order to distinguish these
particular functions, we here adopt the dotted line as
shown in Figures 6 and 7.
In fact, our current WS toolkit written in Haskell can
be carried out to do slicing process for source codes of C,
Java and Haskell, whose main interface is shown in Fig-
ure 8.
There are two frames in Figure 8 for displaying codes.
The left frame shows source codes and the right one
shows sliced codes. In Figure 8, for example, a Haskell
Figure 5. A C source code (in left column) and its sliced
code for “fun3” (in right column).
Figure 6. The FDG of the source code in Figure 5.
Figure 7. The FDG of slicing for “fun3” code in Figure 6.
Copyright © 2010 SciRes. IJCNS
882 Y. Z. ZHANG ET AL.
Figure 8. The main interface of our WS toolkit.
source code is showed in the left frame and a sliced code
is showed in the right frame. The sliced code is result of
backward slicing from the slicing node “helloWorld”.
From the sliced code, it can be seen that function “hel-
loWorld” depends on function “changeStr”. Therefore,
both the definitions about function “helloWorld” and
function “changeStr” have been remained in the sliced
As showed in above examples, some functions such as
auxiliary functions in source codes, may not have good
interface to be published as a WS. Program slicing tech-
nology can compose several services and generate their
codes, but it has no ideal method to recognize functions
which have good interface. How can we recognize such
functions? In fact, users who upload source codes know
it clearly. Therefore, it is helpful when users give a
WSDP (Web Service Description for Publishing) file to
describe which functions in a source code to be pub-
lished as web services.
3.2. WSDP Files
A WSDP (Web Service Description for Publishing) file,
which states what functions to be published as web ser-
vices, is written in the XML file format so that it can be
easily embedded into WS framework.
Before slicing the source codes, WSDP files should be
parsed to obtain some useful information. The data type
WSDPInfo is defined as follows to record the useful in-
formation in a WSDP file.
data WSDPInfo =
(MainFileName, Authors, Operator, FuncName,
Where the types MainFileName, Authors and Operator
describe the basic information of a source file. The type
FuncName records the names of functions wanted to be
published as a service and the FuncDoc describes some
information of each service.
An example of a WSDP file can be found in Figure 9.
Through parsing the WSDP file in Figure 9, we can
know those functions’ names that will be published as
services and some other useful information.
As is well known, the WSDL document of a service is
very useful when the service is published. Based on the
slicing process and result, we discuss in next section to
generate a WSDL document for each service to be pub-
4. WS Generation and Composition
4.1. Generation of a WSDL Document
WSDL is an XML-based language that provides a model
for describing web services. It describes the location and
the name of a service as well as the operation or function
the service provides. It contains a series of definitions
about a service. Some major elements of a WSDL
document are listed in Table 1.
Figure 10 shows a simple example of a WSDL docu-
ment. In Figure 10, the <portType> element defines
“Version” as a port name, “getVersion” as an operation
name. The operation “getVersion” has an input message
named “getVersionRequest” and an output message
named “getVersionResponse”.
In order to generate a WSDL document more conven-
iently, we define as follows the date type Opr_Info to
record the content of the important elements in a WSDL
Figure 9. An example of a WSDP file.
Table 1. The main elements of a WSDL document.
<portType>the operation of a WS
<message>the messages used by a WS
<binding> the transportation protocol
<service> the detail and important information
Copyright © 2010 SciRes. IJCNS
data Opr_Info
= (Opr_InN, Opr_InT, Opr_OutT, Opr_Name)
The type Opr_Info has four child types: Opr_InN (in-
put parameter names), Opr_InT (input parameter types),
Opr_OutT (return value’s type) and Opr_Name (the
name of an operation).
The type Opr_Info can be obtained through parsing
source codes, and Figure 11 shows the process of gener-
ating elements <message> and <portType> from type
For example, if there is a function named “hello” be-
low to be published as a WS.
String hello (String name)
printOutString (“welcomg:”+ name);
The corresponding Opr_Info type for the function
“hello” is: Opr_Info = {Opr_InN = name, Opr_InT =
String, Opr_OutT = String, Opr_Name = hello}. The
WSDL elements <message> and <portType> of “hello”
function are shown in Figur e 1 2 .
The WSDL element <binding> describes the related
protocols and the format of the messages for each port. It
tells a server which styles are used to transfer messages
Figure 10. An example of a WSDL document.
Figure 11. The part of a WSDL document generated from
an Opr_Info type.
Figure 12. The WSDL <message> and <portType> of the
example function “hello”.
between the server and a client. Figure 13 shows the
WSDL <binding> of the example function “hello” above.
Here we choose RPC (Remote Procedure Call) as the
transmission style.
The WSDL element <service> describes the detail in-
formation of a service, such as its name and web address.
For example, supposing the server address of the “hello”
function is “http://localhost:8080/axis/Hello.jws”, we will
get such WSDL <service> descriptions as shown in Fig-
ure 14.
Since the generations of the WSDL element <message>,
<portType>, <binding>, <service> has been introduced
above, the generation of a WSDL document would be
very easy by composing them together.
Our WS toolkit has a “WSDL” menu to generate
WSDL documents for the functions to be published. For
the example code in Figure 8, the WSDL menu in Fig-
ure 15 has three submenu items named “helloWorld”,
“factorial” and “bind2”, which are chosen by its WSDP
file in Figure 9. Since the WSDP file does not list
“changeStr” as a service to be published, the WS toolkit
only generates WSDL documents for these three func-
tions. Figure 16 gives the result of the WSDL document
generated for the “helloWorld” function.
4.2. Generation of SOAP Messages
Simple Object Access Protocol (SOAP) [27-29] is a sim-
ple XML-based protocol that allows applications to ex-
change information over HTTP. Simply speaking, SOAP
is a protocol which is used to access web services, and its
message is simple XML documents.
RPC [30] is now used by current applications such as
DCOM and CORBA to communicate with each other.
Figure 13. The WSDL <binding> of the “hello” function.
Figure 14. The WSDL <service> of the “hello” function.
Copyright © 2010 SciRes. IJCNS
884 Y. Z. ZHANG ET AL.
Figure 15. The WSDL menu in the WS toolkit.
Figure 16. The result of generating WSDL for “helloWorld”
from our WS toolkit.
However, it’s not designed for HTTP. Because of com-
patibility and security issues, RPC is always be blocked
by firewall and proxy servers.
An alternative way to communicate between applica-
tions is using HTTP with supporting by almost all
browsers and servers. Based on HTTP, SOAP provides
some standard functions to make applications communi-
cate to each other, so it make web services more hetero-
geneous than web applications. Web applications use
multiple programming languages, but web services can
also use different operating systems, different server
When users want to use a published service, they can
send requests to a server through SOAP messages. A
SOAP message contains the operation name and related
parameter values of a service. It can be generated by
parsing the WSDL document of a service. For simplicity,
the SOAP messages instantiated in this paper only con-
tains two required elements <envelope> and <body>
shown in Table 2.
Figure 17 shows the relationship between WSDL and
SOAP with three document fragments. Fragment 1 is the
<message> and <portType> elements of a WSDL docu-
ment. Fragment 2 is a SOAP message, and Fragment 3 is
the <operation> element of a WSDL. The arrows indi-
cate how to use a WSDL document to generate a SOAP
message. For example, names and types of the parame-
ters in <body> element of Fragment 2 come from the
<message> element of Fragment 1.
Figure 18 shows the process about how to generate a
SOAP message from a WSDL document.
In practice, we encapsulate the information a SOAP
message need into a data type SOAP_Info when parsing
a WSDL document.
data SOAP_Info
= (In_Para, Out_Para,Opr_Name, In_Ns, Out_Ns)
Table 2. The main elements of a SOAP message.
<envelope>REQUIREDimplies this is a SOAP message
<header> OPTIONALcontains some header messages
<body> REQUIREDcontains request and response
<fault> OPTIONALprovides messages dealing with
Figure 17. Relationship between WSDL (Fragment 1 and
Fragment 3) and SOAP (Fragment 2).
Copyright © 2010 SciRes. IJCNS
Figure 18. The process of generating a SO AP message from a
WSDL document.
The SOAP_Info type has five child types. In_Para (or
Out_Para) records the parameters’ names and types of a
service’s input (or return value). Opr_Name describes
the names of the operations in a SOAP message. The
In_Ns/Out_Ns type is related with the namespace of a
SOAP request/response. Based on the SOAP_Info type, a
SOAP message can be generated and then be sent to the
related WS.
4.3. Procedure of SOAP Transmission
In this subsection, we will discuss how to send the SOAP
message generated from a WSDL document to a server.
As is known that SOAP is based on HTTP, we just need
to seed a HTTP packet in which a SOAP message is en-
capsulated to the server related.
Before sending SOAP messages to a server, the
server’s location address, which is usually called end-
point, must be known. This endpoint can also be ana-
lyzed from WSDL documents by parsing the <service>
The element <service> describes some detail and im-
portant information of a service. For example, from Fig-
ure 19, we know that the element <service> describes the
name and the port of a service as well as the location ad-
dress. So from the WSDL element <service>, we can eas-
ily obtain the location address (endpoint) of the transmis-
sion destination of a SOAP message.
Once a server receives a request SOAP message, the
server will generate a response SOAP message with the
result of calling the specific operations.
For example, Figures 20-21 give a request and its re-
sponse SOAP message respectively. For simplicity, we
here only show the elements <body> of SOAP messages,
and omit their other elements such as <envelope>.
There’s no information about input parameters in Figure
20 because the “getVersion” operation doesn’t needs any
Furthermore, Figure 22 shows the procedure of send-
ing and receiving SOAP messages, each of which is
packaged into a HTTP packet when transmitted between
users and servers.
When calling an operation of a service, an important
function “runService” below is used to send HTTP pack-
ets to servers, with passing parameters to the operation of
a service and returning its result values. Through such
operations, communication between users and server can
be established.
runService request =
Request request;
-- package a SOAP message, named request
Figure 19. A <service> element of a WSDL document.
Figure 20. An example request SOAP message.
Figure 21. An example response SOAP message.
Figure 22. The procedure of SOAP transmission.
Copyright © 2010 SciRes. IJCNS
886 Y. Z. ZHANG ET AL.
result = simpleHTTP request operation;
-- use the simpleHTTP function to
-- send request package
case result of
error putout (“service error+ error);
right soap case soap of
-- if right, return response SOAP message
-- and parse it
error putout (“soap error+ error);
right body getbodyContent body;
-- if right, get the body content
4.4. Proxy Services
In practical applications, to automatically run the above
functions of generating WSDL document and SOAP
messages, we often introduce the function of a proxy
service. If such a proxy service has been developed, us-
ers only need to provide the parameters of a service op-
eration to its proxy service, and the server will automati-
cally call related functions to generate WSDL documents
and SOAP messages with the result of the service opera-
tion. To ensure that the proxy service can work properly,
all of the data transmission and display should be based
on XML. So the types of a service operation must be
converted into XML-format types.
There is only one data type named string in XML
since XML is based on text. Therefore, all data types of a
service must be converted into an XML-format type. To
fulfill such requirement, a class is defined as follows.
class Xmlable a where
toContent :: a
fromContent :: [[ Content]]
In the Xmlable class, there are two operations: toCon-
tent and fromContent, which aims at converting an arbi-
trary type, a, into an XML-format type, and restoring an
arbitrary type form a non-original XML format respec-
tively. The toContent function can automatically convert
the operation parameters of a service into XML-format
as long as it is declared as an instance of Xmlable.
In fact, the function “runService” mentioned in Sub-
section 4.3 is a prototype of proxy service. It has only
one parameter named SOAP_Info which can be gener-
ated form a SOAP request message. Prefix “ws_” is
added to a service name as its proxy service’s name. All
data types of a service must be declared as instances of
class Xmlable when generating a proxy service for a ser-
vice. Servers will call the proxy service directly and get
the operation’s return value.
A simple example of generating a proxy service can be
found below.
hello:: String
hello str = welcome ++ str
-- Server generates a proxy service name ws_hello:
ws_hello soapinfo = runService soapinfo
Instance Xmlable String
-- declare type String as an instance of Xmlable
5. Conclusions & Future Work
5.1. Conclusions
This paper introduces the method about how to generate
and compose services using program-slicing technology
based on function dependence graph. Through parsing
source codes, sliced codes for each service can be gener-
ated. It also introduced the method about how to generate
WSDL documents and SOAP messages through sliced
codes of each service.
To make sure web services in a server work smoothly,
we generate a proxy service/function for each service.
Users can call a WS by accessing the proxy function of
that service. In addition, we have introduced the SOAP
transmission between users and servers.
5.2. Future Work
This paper has proposed how to generate and compose
services and how to generate WSDL documents and
SOAP messages. However, no mechanism about how to
publish a service is introduced. Users who want to access
a service must know the endpoint of the service. But we
haven’t distributed an endpoint for each service on a
HTTP server. Therefore, an important part of our future
work is to publish a service on servers.
Another part of our future work is to study BPEL4WS
(Web Services Business Process Execution Language for
Web Service, which is also based-on-XML language)
[31], and to generate corresponding operation dependence
graph from a BPEL4WS file. BPEL4WS specifies inter-
actions with web services. Through an operation de-
pendence graph, we can verify the consistency of the
composition of some services and evaluate their compo-
sition quality.
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