A Brief History of Database Applications
We now give a brief historical overview of the applications that use DBMSs and how these applications provided the impetus for new types of database systems.
1. Early Database Applications Using Hierarchical and Network Systems
Many early database applications maintained records in large organizations such as corporations, universities, hospitals, and banks. In many of these applications, there were large numbers of records of similar structure. For example, in a university application, similar information would be kept for each student, each course, each grade record, and so on. There were also many types of records and many interrelationships among them.
One of the main problems with early database systems was the intermixing of conceptual relationships with the physical storage and placement of records on disk. Hence, these systems did not provide sufficient data abstraction and program-data independence capabilities. For example, the grade records of a particular student could be physically stored next to the student record. Although this provided very efficient access for the original queries and transactions that the database was designed to handle, it did not provide enough flexibility to access records efficiently when new queries and transactions were identified. In particular, new queries that required a different storage organization for efficient processing were quite difficult to implement efficiently. It was also laborious to reorganize the database when changes were made to the application’s requirements.
Another shortcoming of early systems was that they provided only programming language interfaces. This made it time-consuming and expensive to implement new queries and transactions, since new programs had to be written, tested, and debugged. Most of these database systems were implemented on large and expensive mainframe computers starting in the mid-1960s and continuing through the 1970s and 1980s. The main types of early systems were based on three main paradigms: hierarchical systems, network model based systems, and inverted file systems.
2. Providing Data Abstraction and Application Flexibility with Relational Databases
Relational databases were originally proposed to separate the physical storage of data from its conceptual representation and to provide a mathematical foundation for data representation and querying. The relational data model also introduced high-level query languages that provided an alternative to programming language interfaces, making it much faster to write new queries. Relational representation of data somewhat resembles the example we presented in Figure 1.2. Relational systems were initially targeted to the same applications as earlier systems, and provided flexibility to develop new queries quickly and to reorganize the database as requirements changed. Hence, data abstraction and program-data independence were much improved when compared to earlier systems.
Early experimental relational systems developed in the late 1970s and the commercial relational database management systems (RDBMS) introduced in the early 1980s were quite slow, since they did not use physical storage pointers or record placement to access related data records. With the development of new storage and indexing techniques and better query processing and optimization, their performance improved. Eventually, relational databases became the dominant type of data-base system for traditional database applications. Relational databases now exist on almost all types of computers, from small personal computers to large servers.
3. Object-Oriented Applications and the Need for More Complex Databases
The emergence of object-oriented programming languages in the 1980s and the need to store and share complex, structured objects led to the development of object-oriented databases (OODBs). Initially, OODBs were considered a competitor to relational databases, since they provided more general data structures. They also incorporated many of the useful object-oriented paradigms, such as abstract data types, encapsulation of operations, inheritance, and object identity. However, the complexity of the model and the lack of an early standard contributed to their limited use. They are now mainly used in specialized applications, such as engineering design, multimedia publishing, and manufacturing systems. Despite expectations that they will make a big impact, their overall penetration into the database products market remains under 5% today. In addition, many object-oriented concepts were incorporated into the newer versions of relational DBMSs, leading to object-relational database management systems, known as ORDBMSs.
4. Interchanging Data on the Web for E-Commerce Using XML
The World Wide Web provides a large network of interconnected computers. Users can create documents using a Web publishing language, such as HyperText Markup Language (HTML), and store these documents on Web servers where other users (clients) can access them. Documents can be linked through hyperlinks, which are pointers to other documents. In the 1990s, electronic commerce (e-commerce) emerged as a major application on the Web. It quickly became apparent that parts of the information on e-commerce Web pages were often dynamically extracted data from DBMSs. A variety of techniques were developed to allow the interchange of data on the Web. Currently, eXtended Markup Language (XML) is considered to be the primary standard for interchanging data among various types of databases and Web pages. XML combines concepts from the models used in document systems with database modeling concepts. Chapter 12 is devoted to the discussion of XML.
5. Extending Database Capabilities for New Applications
The success of database systems in traditional applications encouraged developers of other types of applications to attempt to use them. Such applications tradition-ally used their own specialized file and data structures. Database systems now offer extensions to better support the specialized requirements for some of these applications. The following are some examples of these applications:
Scientific applications that store large amounts of data resulting from scientific experiments in areas such as high-energy physics, the mapping of the human genome, and the discovery of protein structures.
Storage and retrieval of images, including scanned news or personal photo-graphs, satellite photographic images, and images from medical procedures such as x-rays and MRIs (magnetic resonance imaging).
Storage and retrieval of videos, such as movies, and video clips from news or personal digital cameras.
Data mining applications that analyze large amounts of data searching for the occurrences of specific patterns or relationships, and for identifying unusual patterns in areas such as credit card usage.
Spatial applications that store spatial locations of data, such as weather information, maps used in geographical information systems, and in auto-mobile navigational systems.
Time series applications that store information such as economic data at regular points in time, such as daily sales and monthly gross national prod-uct figures.
It was quickly apparent that basic relational systems were not very suitable for many of these applications, usually for one or more of the following reasons:
More complex data structures were needed for modeling the application than the simple relational representation.
New data types were needed in addition to the basic numeric and character string types.
New operations and query language constructs were necessary to manipu-late the new data types.
New storage and indexing structures were needed for efficient searching on the new data types.
This led DBMS developers to add functionality to their systems. Some functionality was general purpose, such as incorporating concepts from object-oriented data-bases into relational systems. Other functionality was special purpose, in the form of optional modules that could be used for specific applications. For example, users could buy a time series module to use with their relational DBMS for their time series application.
Many large organizations use a variety of software application packages that work closely with database back-ends. The database back-end represents one or more databases, possibly from different vendors and using different data models, that maintain data that is manipulated by these packages for supporting transactions, generating reports, and answering ad-hoc queries. One of the most commonly used systems includes Enterprise Resource Planning (ERP), which is used to consolidate a variety of functional areas within an organization, including production, sales, distribution, marketing, finance, human resources, and so on. Another popular type of system is Customer Relationship Management (CRM) software that spans order processing as well as marketing and customer support functions. These applications are Web-enabled in that internal and external users are given a variety of Web-portal interfaces to interact with the back-end databases.
6. Databases versus Information Retrieval
Traditionally, database technology applies to structured and formatted data that arises in routine applications in government, business, and industry. Database technology is heavily used in manufacturing, retail, banking, insurance, finance, and health care industries, where structured data is collected through forms, such as invoices or patient registration documents. An area related to database technology is Information Retrieval (IR), which deals with books, manuscripts, and various forms of library-based articles. Data is indexed, cataloged, and annotated using key-words. IR is concerned with searching for material based on these keywords, and with the many problems dealing with document processing and free-form text processing. There has been a considerable amount of work done on searching for text based on keywords, finding documents and ranking them based on relevance, automatic text categorization, classification of text documents by topics, and so on. With the advent of the Web and the proliferation of HTML pages running into the billions, there is a need to apply many of the IR techniques to processing data on the Web. Data on Web pages typically contains images, text, and objects that are active and change dynamically. Retrieval of information on the Web is a new problem that requires techniques from databases and IR to be applied in a variety of novel combinations. We discuss concepts related to information retrieval and Web search in Chapter 27.
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