Schema Evolution publication categorizer

We consider the problem of XML Schema evolution. In the ever-changing context of the web, XML schemas continuously change in order to cope with the natural evolution of the entities they describe. Schema changes have important consequences. First, existing documents valid with respect to the original schema are no longer guaranteed to fulfill the constraints described by the evolved schema. Second, the evolution also impacts programs, manipulating documents whose structure is described by the original schema.

Schema evolution is the increasingly important ability to adapt deployed schemas to changing requirements. Effective support for schema evolution is challenging since schema changes may have to be propagated, correctly and efficiently, to instance data and dependent schemas, mappings, or applications.

Context
UML and XML are two of the most commonly used languages in software engineering processes. One of the most critical of these processes is that of model evolution and maintenance. More specifically, when an XML schema is modified, the changes should be propagated to the corresponding XML documents, which must conform with the new, modified schema.
Objective

This chapter describes how you can update your XML schema after you have
registered it with Oracle XML DB. XML schema evolution is the process of updating
your registered XML schema.
This chapter contains these topics:
■ Overview of XML Schema Evolution
■ Using Copy-Based Schema Evolution
■ Using In-Place XML Schema Evolution.

The W3C XML Schema recommendation defines the structure and data types for XML documents, but lacks explicit support for time-varying XML documents or for a time-varying schema. In previous work we introduced τXSchema, which is an infrastructure and suite of tools to support the creation and validation of time-varying documents, without requiring any changes to XML Schema. In this paper we extend τXSchema to support versioning of the schema itself.

The W3C XML Schema recommendation defines the structure and data types for XML documents.
XML Schema lacks explicit support for time-varying XML documents or for time-varying schemas. An
XML document evolves as it is updated over time or as it accumulates from a streaming data source. A
temporal document records the entire history of a document rather than just its current state or snapshot.
Capturing a document’s evolution is vital to providing the ability to recover past versions, track changes

Schema evolution is of two kinds: (a) those requiring instance transformation because the application is simpler to develop when it works only with one version of the schema, and (b) those in which the old data must be preserved and instance transformation must be avoided. The latter is important in practice but has received scant attention in the literature. Data conforming to multiple versions of the XML schema must be maintained, indexed, and manipulated using the same query. Microsoft’s SQL Server 2005 introduces XML schema collections to address both types of schema evolution.

A major advantage of Service-Oriented Architectures (SOA) is composition and coordination of loosely coupled services. Because the development lifecycles of services and clients are decoupled, multiple service versions have to be maintained to continue supporting older clients. Typically versions are managed within the SOA by updating service descriptions using conventions on version numbers and namespaces. In all cases, the compatibility among services description must be evaluated, which can be hard, error-prone and costly if performed manually, particularly for complex descriptions.

The ability to cope with multiple competing stakeholders, fluid requirements, emergent behavior, and susceptibility to external pressures that can cause changes across an entire organization, coupled with the ability to support service diversification, is a key to an enterprise’s competitiveness. Web services equip enterprises with the potential to react to change by addressing two interrelated sets of requirements: the ability to accommodate service changes that demand rapid response and to support service variation according to customers’ needs and requirements.

Many XML-relational systems, i.e., the systems that use an XML schema as an external schema and a relational schema as an internal schema of the data application representation level, require modifications of the data schemas in the course of time. Schema evolution is one of the ways to support schema modifications for the application at the DBMS level. A number of schema evolution support systems for different data models have been suggested.

The Semantic Web has the ambitious goal of enabling complex autonomous applications to reason on a machine-processable version of the World Wide Web. This, however, would require a coordinated effort not easily achievable in practice. On the other hand, spontaneous communities, based on social tagging, recently achieved noticeable consensus and diffusion.

Most available approaches for XML schema evolution spec-
ify the evolution steps for an XML schema or a DTD. This article will
show that schema evolution can also be realized on a conceptual model.
Schema evolution always requires propagating the changes to the XML
documents that are already associated to the schema. This article sug-
gests a method for conceptual schema evolution concerning all these
subtasks. It is implemented in a tool called CoDEX (Conceptual Design
and Evolution of XML schemas).

Web Services are designed for loosely coupled systems, which means that in many cases it is not possible to synchronously upgrade all peers of a Web Service scenario. Instead, Web Service peers should be able to coexist in different versions. Additionally, older software versions often could benefit from upgrades to the service if they were able to understand it. This paper presents a framework for semantically extensible schemas for Web Service evolution. The core idea of is to use declarative semantics to describe extensions to a service's vocabulary.

There is much current interest in publishing and viewing databases as XML documents. The general benefits of this approach follow from the popularity of XML and the tool set available for visualizing and processing information encoded in this universal standard. In this paper, we explore the additional and unique benefits achieved by this approach on temporal database applications. We show that XML views combined with XQuery can provide surprisingly effective solutions to the problem of supporting historical queries on past content of database relations and their evolution.

Time is a pervasive dimension of reality as everything evolves as time elapses. Information systems and applications at least mirror, and often have to capture, the time-varying and evolutionary nature of the phenomena they model and the activities they support. This aspect has been acknowledged and long studied in the field of temporal databases but it truly applies also to the World Wide Web, although it has not seemingly considered as a primary issue yet.

One of the main challenges in data integration systems is the maintenance of the mappings between the mediation schema and the source schemas. In a dynamic environment, such mappings must be flexible enough in order to accommodate new data sources and new usersrsquo requirements. In this context, we address a novel and complex problem that consists in propagating a change event occurring at the source level or at the user level into the mediation level.

XML is designed for the creation of languages based upon self-describing markup. The inevitable evolution of these languages is called versioning. Versioning means adding, deleting, or changing parts of the language. Making versioning work in practice is one of the most difficult problems in computing, with a long history of failed attempts.

In our emerging digital paper-less society, massive amount of information is being maintained in on-line repositories and diverse web site representations of this information must be served over the Internet to different user groups. E-commerce and digital libraries are two representative sample applications with such needs. In this paper we present a database-centric approach called Re-Web that addresses this need for flexible web site generation, re-structuring, and maintenance. Re-Web is based on two key ideas.

As information on the world wide web continues to proliferate at an astounding rate, the extensible markup language (XML) has been emerging as a standard format for data representation on the web. In many applications, specific document type definitions (DTDs) are designed to enforce a semantically agreed-upon structure of the XML documents for management.

The advent of web services that use XML-based message exchanges has spurred many efforts that address issues related to inter-enterprise service electronic commerce interactions. Currently emerging standards and technologies enable enterprises to describe and advertise their own Web Services and to discover and determine how to interact with services fronted by other businesses. However, these technologies do not address the problem of how to reconcile structural differences between similar types of documents supported by different enterprises.

The structure of XML documents, expressed as XML schemas [6], can evolve as well as their content. Systems must be frequently adapted to real-world changes or updated to fix design errors and thus data structures must change accordingly in order to address the new requirements. A consequence of schema evolution is that documents instance of the original schema might not be valid anymore. Currently, users have to explicitly revalidate the documents and identify the parts to be updated. Moreover, once the parts that are not valid anymore have been identified, they have to be explicitly updated.

Designers of XML formats have to face the problem of how to design their formats to be extensible and yet be resilient to changes due revisions of the format. This presentation covers various techniques and considerations for versioning XML formats.

As information on the World Wide Web continues to proliferate at an astounding rate, the Extensible Markup Language (XML) has been emerging as a standard format for data representation on the web. In many application domains, specific document type definitions (DTDs) are designed to enforce a semantically agreed-upon structure of the XML documents. In XML context, these structural definitions serve as schemata.

This paper deals with updates of XML documents that satisfy
a given schema, e.g., a DTD. In this context, when a given update
violates the schema, it might be the case that this update is accepted,
thus implying to change the schema. Our method is intended to be used
by a data administrator who is an expert in the domain of application of
the database, but who is not required to be a computer science expert.
Our approach consists in proposing different schema options that are
derived from the original one. The method is consistency-preserving:

XML documents are a typical kind of semistructured data. The usage of XML has increased significantly since 1998, when the XML recommendation was released. The structure of XML documents can be described using a Document Type Definition (DTD). Documents are called valid documents if their structure corresponds to a DTD. If the structure of a DTD changes, it is desirable to apply these changes to documents that are valid with respect to this DTD. These transformations are called evolution. This paper shows how different changes to the DTD effect XML documents.