第8章データ管理

OODBMSs appeared around 1985 and originated as extensions of OO programming languages. Object-oriented programmers store the developed products as objects and modify existing objects to make new objects within the OODBMS. OODBMSs store persistent objects in a transparent way, support persistence orthogonality, and guarantee the ACID properties. OODBMS has many limitations such as lack of a universal data model, lack of experience compared to RDBMS, lack of support, and complexity. The object data management group (ODMG) was created in 1991 and is based on object management group (OMG) standard; its main idea is to create a set of specifications to develop applications for an object database. There have been five revisions of ODMG and the last version is ODMG 3.0. Most mainstream database applications are built using an OO programming language in combination with an RDBMS rather than using an object-relational mapping (ORM).

MongoDB is the most popular NoSQL database; it has delivered substantial values for some businesses that have been struggling to handle their unstructured data with the traditional RDBMS approach. After MetLife spent years trying to build a centralized customer database on a RDBMS that could handle all its insurance products, someone at an internal hackathon built one with MongoDB within hours, which went to production in 90 days.

Extended relational databases (ERDBMSs) combine characteristics of RDBMS and OODBMS. The products of ERDBMSs provide a relational data model and query language that have been extended to include features of OODBMSs.

The relational model has a flat structure, and expensive joins are needed to defragment the data before it can be successfully used, which increases the complexity of the objects due to normalization. Specialization, categorization, and aggregation cannot be directly supported. A tuple constructor can only be used on atomic values while a set constructor can only be used on tuples; however, both constructors are not orthogonal, cannot model behavior or store functions, and both provide poor support for multimedia.

A trigger is a statement consisting of declarative and/or procedural instructions and is stored in the catalog of the RDBMS. Triggers can also reference attribute types in other tables. Triggers are automatically executed when a triggering event occurs such as any change in the database. Triggers are similar to procedures stored in the database but differ in that they need to be explicitly invoked. Triggers are easy to code, are useful in the validation process, allow calling other procedures from the trigger, and allow recursion.

Object-relational DBMSs (ORDBMSs) keep the relation as the fundamental building block and SQL as the core DDL/DML, but they use the following OO extensions: user-defined types (UDTs), user-defined functions (UDFs), inheritance, behavior, polymorphism, collection types, large objects (LOBs), and recursive SQL queries.

You are told that a new type of data structure has been unveiled and that it characterizes new forms of data being collected from sensors located at the edge of the network.

Would you conclude that a new kind of nonrelational database management system needs to be developed? What would be your approach for selecting the best possible type of nonrelational database management system for this application?

Extensible Markup Language (XML) is a markup language similar to HTML, but users define their tags; predefined tags such as HTML are not used. The oldest schema language for XML is the document type definition (DTD). An XML Schema is the metadata that describes the structure of an XML document. Extensible Stylesheet Language (XSL) defines the features and syntax of XML and consists of a language for transforming XML documents (XSLT) and an XML vocabulary for specifying formatting (XSL-FO). An XML namespace is a collection of names that can be used as element names in an XML document. XML Path Language (XPath) uses path expressions to select nodes in an XML document. An XML database is a data persistence system whereby the data are specified and stored in XML format. It is easy to code but has no universally accepted rules for the XML database.