XML EVERY-FLAVOR TESTING

Antonia Bertolino, Jinghua Gao, Eda Marchetti

ISTI-CNR

Via Moruzzi 1, 56124 Pisa

Keywords:

Application testing, conformance testing, DTD, XML, XML Schema.

Abstract:

With XML and XML Schema widely acknowledged as the de facto standard for data exchange and interop-

erability between remote applications, the need for checking integrity and adequacy of XML documents, also

by means of automated tools, increases. In this perspective, this paper addresses two objectives: we provide a

classiﬁcation and a short overview of the diverse existing approaches for the testing of XML-based documents;

then, pushing further the potential of XML for testing purposes, we pursuit the application of traditional test-

ing methods to programs using XML input data. We discuss the use of XML and XML schema as a basis for

formalizing and automatizing the testing of applications using such kind of data, with particular reference to

recent proposals for speciﬁcation-based and perturbation-based testing approaches.

1 INTRODUCTION

In the pursuit of working interoperability among inde-

pendently developed systems, industry is increasingly

adopting open speciﬁcations and binding such spec-

iﬁcations to standardised technologies. Such bind-

ing technologies must be open in nature, to allow

for a wide range of diverse platforms, languages, and

tools to be used, and still create compliant applica-

tions and content. The XML (eXtensible Markup

Language)(W3CXML, 1996) is today the predomi-

nant format for data representation and is generally

recognized as the standard way to exchange informa-

tion between remote systems and to bind the speciﬁ-

cations (W3C, 2005).

As well as the XML documents (also known as in-

stances), the W3C has developed speciﬁcations for

creating “control documents” that are used to de-

ﬁne the structure of XML documents themselves.

These speciﬁcations - ﬁrst Document Type Deﬁnition

(DTD) (DTD, 1996) and later XML Schema (XSD)

(W3CXMLSchema, 1998) allow parties to construct

vocabularies of tags for particular types of documents,

and to insist on particular structuring rules.

Paired with XML diffusion, the DTDs and XML

Schema have largely spread up. DTDs and XML

Schemas are used for expressing basic structural rules

and complex restrictions of the diverse data and pa-

rameters that units/components exchange with each

other: both of them can be considered as the struc-

turing schema of XML documents. The introduction

of XML ﬁrst, and of XML structuring schemas then,

paved the way for a lot of tools and techniques de-

voted to check the most varied aspects and concerns

of the produced documents. In fact, in parallel with

the establishment of common formats for data ex-

change, and the standardization of parameters in com-

munication interfaces, the need grew for ensuring the

quality and integrity of the produced documents, as

well as for validating that the XML products do con-

form, from a syntactical viewpoint, to the established

standard formats and schemas, and, if feasible, also

to the intended semantics. We refer broadly to the

whole variety of developed technologies as “XML-

based testing”. However, the kind of veriﬁcations

pursued, and the approaches and tools adopted vary

far and wide from case to case. Besides, the various

techniques are not alternative, but depending on the

speciﬁc application can be combined in several inter-

esting ways.

As is further discussed in this paper, the introduc-

tion of formalized and standardized formats for input

data representation allows for a wealth of checks, and

not all its potential has been explored so far. In this

context, this paper focuses on two objectives:

1. For aim of clariﬁcation we provide a classiﬁcation

268

Bertolino A., Gao J. and Marchetti E. (2006).

XML EVERY-FLAVOR TESTING.

In Proceedings of WEBIST 2006 - Second International Conference on Web Information Systems and Technologies - Inter net Technology / Web

Interface and Applications, pages 268-273

DOI: 10.5220/0001254602680273

 SciTePress

of the diverse existing approaches, organized into

a logical structure based on their varying types of

veriﬁcation.

2. From the above classiﬁcation it is clear that the

enormous potential of XML and similar language is

only marginally exploited for testing purposes. We

propose to use XML and XML Schema for ”for-

malizing” the testing of the applications which use

such kind of data.

In the next section we overview existing ap-

proaches, distinguishing between approaches that are

applied to the XML documents, and approaches that

start from the XML Schema. Then, in Section 3,

we look at the future, by discussing the potential of

leveraging application test techniques with automated

tools relying on XML input data. Finally, we draw

conclusions and hint at future work.

2 A TOPOGRAPHY

The term XML-based testing acquires different mean-

ings both in common sense and in literature. It can

refer to verifying the adequacy of a XML document

with respect to the users exigencies; verifying the ad-

equacy of a XML instance with respect to a speciﬁc

schema (DTD or XML schema); verifying the well-

formedness of a schema structure; or even for deﬁn-

ing methodologies for merging or matching diverse

XML schemas.

In this vast context of diverse interpretations, this

paper tries to classify the various testing approaches

and represent them into a structured form (Figure 1).

We identify ﬁrst a course division of XML-based test-

ing into XML documents testing and schema based

testing. We provide the reader with a brief deﬁnition

of what is understood for XML-based testing in the

various nodes of the tree, and a tentatively complete

overview of the literature.

2.1 Testing XML Documents

Over the years, XML format ﬂexibility and its possi-

bility to be adapted to any kind of situation increased

the possibility to use it into diverse customized do-

mains as well as for data interchange for web-sites,

graphics, remote and real time applications.

With the aim of developing successful applications,

which can correctly interoperate each other, verifying

the correctness and adequacy of XML data becomes

extremely important. For this diverse approaches

have been deﬁned as detailed in the rest of this sec-

tion.

2.1.1 Well-formedness of XML Document

Due to its ﬂexible schema, XML leaves to its users a

certain freedom in writing their speciﬁc documents.

With the aim of interoperability the W3C XML Core

Working Group(W3C, 2005) provides a sort of core

infrastructure that can be used for verifying the XML

document. This is represented by a set of XML-based

guidelines that provide metrics for determining the

conformance to the W3C recommendations (W3C,

2005)

A ﬁrst essential test that must be assessed on an

XML ﬁle instance is called well-formedness (a simi-

lar test is also conducted for XML Schema, see later).

This is a basic requirements for an XML ﬁle, if this

property is not satisﬁed the tested ﬁle cannot even be

classiﬁed as an XML ﬁle. Well-formedness can be

easily veriﬁed, also a simple browser generally pro-

vides conformance validation features for such kind

of validation, however well-formedness does not give

enough guarantees on the quality of an XML ﬁle.

Using as a basis such kind of testing indications,

different sets of test suites have been implemented, for

instance (XMLTestSuite, 2005),(NIST, 2003). Each

of them is represented by a test ﬁle (including up to

diverse thousands of tests) generally associated with

a test report, which contains all the background infor-

mation for verifying a speciﬁc aspect of the confor-

mance of the XML document to the basic recommen-

dations.

2.1.2 Compliance to Speciﬁed Requirements

Along with more and more implementations using it,

in order to realize the information exchange and tran-

sition between the different systems, XML documents

need to conform to requirements coming from dif-

ferent domains. The requirements can derive from a

standard or consist of some speciﬁc rules deﬁned by

the developers community, which can represent the

speciﬁcation of input domain or other requirements

of the system.

Basically the target of the compliance are document

veriﬁcation and validation. Document veriﬁcation is

used to verify that the messages generated by the sys-

tem are conforming to the input standard. Document

validation instead is used to check the conformance of

the content and structure of the documents, and for-

mat the documents to the requirements.

For the automatic veriﬁcation and validation tools

have been implemented, such as (RTTS, nd) which

developed strategies for automated production of re-

quest XML documents for posting to facilitate the

testing of web services and components to facilitate

the validation of data content of XML documents;

(XMLUnit, 2003) which enables unit testing of XML,

and compare a control XML document to a test docu-

XML EVERY-FLAVOR TESTING

269

XML Based Testing

Adopting perturbation

testing

Specification

based testing

Generation of

conforming XML

instances

Verifying XML

documents against

the schema structure

Well-formedness

of XML schema

Using derived

schemas

Compliance

to specified

requirement

Well-formedness

of XML document

Schema Based Testing

Testing XML Documents

Applying testing strategy

for XML-based test generation

Integrating

and matching

schemas

Figure 1: XML Based Testing.

ment to do the validation; (XMLTester, 2002), (XM-

LValidator, 2005), which use different methodologies

to for large, complex systems.

2.1.3 Using Derived Schemas

When a vast amount of information must be manipu-

lated and organized having a common reference struc-

ture is extremely important. For overcoming these

problems, research on how to derive a common struc-

ture from XML instances is going on actively and

interesting result have been produced (Levy, 1999),

(Shanmugasundaran et al., 1999), (Widom, 1999),

(Goldman and Widom, 1997). Recent applications

of this technologies are (Shafazand and Tjoa, 2002),

(Wang et al., 2000), which extract schema using some

graphs according to the frequency of element occur-

rence in XML documents and (Hagen et al., 2004)

in which the authors represent, by using the XML

markup, a text type schema deﬁnition of the structure

of the scientiﬁc paper.

In parallel with these approaches, another ﬁeld of

research, also called instance-level matching (Rahm

and Bernstein, 2001), tries to derive a common struc-

ture by dynamically analyzing the diverse XML el-

ements and extracting from time to time the proper

schema structure. For implementing such kind of

analysis diverse proposals have been adopted such as

rules, neural networks, and machine learning tech-

niques (Berlin and Motro, 2001), (Doan et al., 2000),

(Doan et al., 2001), (Li and Clifton, 1994), (Li and

Clifton, 2000), (Li et al., 2000).

2.2 Schema Based Testing

Many programs set their special requirements on the

XML ﬁle, and can work only if the ﬁles conform to

their speciﬁcations. Currently there are two solutions

that are most popular to this dilemma. One is docu-

ment type deﬁnition (DTD), another is XML schema,

which became an ofﬁcial W3C recommendation in

May 2001.

Establishing in fact a formalized agreement on the

format of data exchange supports the application of

testing strategies for checking the local data structures

and the interfaces used by the different components.

Using a DTD or XSD allows a recipient of an XML

instance to determine whether that instance conforms

to the control document by testing the XML instances

for conformance against control documents. DTDs

and XSDs have been the ﬁrst step towards testing

for the conformance of content and applications. Li-

braries such as Xerces provide speciﬁc interfaces for

document validation and many editors are today avail-

able fort assist the XML instance developer writing

instances conforming, for construction, to an XML

Schema.

The recent literature collects several contributions

dealing with testing of DTD and XML schema.

Schema based testing can be divided into:

- well-formedness,

- Verifying XML documents against the schema struc-

ture,

- Generation of conforming XML documents from

Schema.

2.2.1 Well-formedness of XML Schema

Several XML schema validators for checking the syn-

tax and the structure of the W3C XML Schema docu-

ment are available. Among them, widespread used

are SQC (Schema Quality Checker) (SQC, 2001),

XSV (XML Schema Validator) (W3CXMLValidator,

2001), and XML Spy5 (XMLSpy, 2005). Recently

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an interesting approach has been proposed by (Li and

Miller, 2005), which detects semantic errors in XML

schemas by using mutation analysis.

2.2.2 Verifying XML Documents Against the

Schema Structure

XML validation means checking the conformance of

structure and data in an XML document against dif-

ferent speciﬁcations or protocols models.

Different XML documents can use different

schemas (DTD or XML Schemas) to specify the valid

(what they can do) and invalid (not allowed) docu-

ments. In this case a XML document can be con-

sidered valid only if everything in the document con-

forms to the declarations in schema. For this usually

a schema should include all the elements, attributes

and entities that can be used in the document as well.

There exist several tools to verify the XML docu-

ments against its DTD or XML Schema. For instance,

(Boobna and de Rougemont, 2004), (XMLBuddy,

nd), (XMLJudge, nd) and (EasyCheXML, nd).

2.2.3 Generation of Conforming XML Instances

The widespread diffusion of XML Schema rises the

proliferation of a lot of tools and methodology for de-

riving XML instances, which represent the allowed

naming and structure of data for component interac-

tion and for service requests. XML instances can be

generated from DTD as well.

Depending on the schema, XML instances can be

manually generated. This could be complicated and a

huge work when schemas are complex. So tools for

automated XML instance generation based on DTD

or XML schema appeared. Some of them generate the

XML instance directly, such as (SunXMLInstance-

Generator, 2003), (XMLGenerator, 1999), (XM-

LXIG, 2004), (Tian et al., 2003). Some tools gener-

ate instances in other notations, like java ﬁles (EJB-

SourceGenerator, 2003), (JavaXMLBindlets, 2003),

C++ classes (XOMA, 2002), or .NET language such

as C and VB.NET (ObjectModelGenerator, 2004).

But most of them generate the instances randomly.

The disadvantage of random generation tools is that

instances cannot cover all possibilities of the schema.

An emerging and innovative research ﬁeld is thus

the application of traditional testing strategies (see

an overview in (Bertolino and Marchetti, 2004)) for

generating suites of XML instances from the XML

Schema structure as introduced in section 3.

2.2.4 Integrating and Matching Schemas

Currently the necessity for applications of managing,

using and transforming diverse structure of XML data

is rising. For facing this problem diverse solutions has

been proposed, which can be classiﬁed depending on

the level at which the integration is performed (Rahm

and Bernstein, 2001).

Generally the integration of diverse schema( DTD

or XML schema) can be done involving all the

schemas or only part of them (Meo et al., 2005). Con-

sider the former, diverse references can be found in

literature which proposed automatic transformations

safeguarding also the semantic matching of the in-

volved schemas (Bergamaschi et al., 1999), (Doan

et al., 2000), (Castano et al., 2001), (Anand and

Wilde, 2005), (Jeong and Hsu, 2001), (Meo et al.,

2005), (Meo et al., 2003), (Boukottaya et al., 2004).

3 XML-BASED TEST

GENERATION

From a tester’s point of view, the XML schema for-

mally expresses the basic rules and complex restric-

tions of data and parameters that the diverse class of

systems and web applications exchange, thus provide

an accurate and formalized representation of the input

domain. The data and parameters that system applica-

tion will exchange, are in fact represented accordingly

to a format suitable for automated processing, which

is clearly a big advantage for testing. However so far

this potentiality has been only partially exploited and

the available tools only implement random generation

of XML instances (sec.2.2.3). Adopting a test strat-

egy for test case derivation will have a double posi-

tive side effect: the generation of more accurate and

mindful XML instance and the improving of automa-

tization in test cases speciﬁcation. In the best of our

knowledge only two works of applying a speciﬁc test

strategies have been proposed which rely on the adop-

tion of partition testing and mutation, respectively.

3.1 Speciﬁcation Based Testing

The speciﬁcation based techniques rely on the struc-

tural properties derived from the program speciﬁca-

tions and different techniques can be used for guid-

ing the section of test data ((Bertolino and Marchetti,

2004)). Considering, in particular the generation of

XML instances from Schema, interesting research

area is represented by equivalence partitioning. This

testing strategy relies on the partitioning of the input

domain into subdomains so that any input within a

subdomain can be taken as a representative for the

whole subset. XML Schema lends itself quite natu-

rally to the application of equivalence partition test-

ing. The subdivision of the input domain into subdo-

mains can be done by exploiting the formalized rep-

resentation of the XML Schema. From the diverse

subdomains identiﬁed, the application of equivalence

XML EVERY-FLAVOR TESTING

271

testing amounts to the systematic derivation of a set

of XML instances.

A ﬁrst work in this direction is XML-based Par-

tition Testing (XPT)(Bertolino et al., 2006). This

method uses the prevalent approach to input do-

main partitioning, the Category Partition method (Os-

trand and Balcer, 1988) combined with techniques of

boundary conditions.

3.2 Adopting Perturbation Testing

In the direction of using commonly adopted testing

strategies for guiding the XML based testing, another

interesting work is (Offutt and Xu, 2004) that presents

a new approach to testing Web services. The au-

thors, taking as a basis the approach in (Lee and Of-

futt, 2001) which presents a technique for using muta-

tion analysis to test the semantic correctness for XML

based component interactions, consider communica-

tion infrastructure of web services, typically XML

and SOAP, and develop new approach to testing them

based on data perturbation.

4 CONCLUSION

We presented in this paper a survey of the existing

approaches for the XML-based testing, trying to clas-

sifying them into a well deﬁned structure. Our intent

was twofold: ﬁrst developing a reference schema that

can be useful to anyone is facing with the vast and

complex world of XML-Based testing. The second

objective was identifying the possible ﬁeld for further

future researches. We in particular focus on the appli-

cation of the commonly used testing strategies taking

as an input the XML Schema structure. This is an

innovative ﬁeld of research that is only partially ex-

ploited but has a lot of potentiality also on view of

automating the test cases generation. As future direc-

tion we want to investigate on this and on the basis of

the works summarized in this paper, developing other

innovative testing proposals. In particular we wan to

focus on some new methodologies for integrating an

combining the diverse existing approaches, such for

instance of 2.1.3 with XPT. Finally thanks to the col-

laboration to diverse university and consortium work-

ing on the e-leaning environment, we want to vali-

date our testing methodologies with case studies taken

from the ﬁeld.

ACKNOWLEDGMENTS

This work has been supported by the European

Project TELCERT (FP6 STREP 507128).

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