In the 1970s and 1980s, attempts were made to build database systems with integrated hardware and software. The underlying philosophy was that such integration would provide higher performance at lower cost. Examples were IBM "System/38, the early offering of "Teradata, and the "Britton Lee, Inc. database machine.
Another approach to hardware support for database management was "ICL's "CAFS accelerator, a hardware disk controller with programmable search capabilities. In the long term, these efforts were generally unsuccessful because specialized database machines could not keep pace with the rapid development and progress of general-purpose computers. Thus most database systems nowadays are software systems running on general-purpose hardware, using general-purpose computer data storage. However this idea is still pursued for certain applications by some companies like "Netezza and Oracle ("Exadata).
Late 1970s, SQL DBMS
IBM started working on a prototype system loosely based on Codd's concepts as System R in the early 1970s. The first version was ready in 1974/5, and work then started on multi-table systems in which the data could be split so that all of the data for a record (some of which is optional) did not have to be stored in a single large "chunk". Subsequent multi-user versions were tested by customers in 1978 and 1979, by which time a standardized "query language – SQL["citation needed] – had been added. Codd's ideas were establishing themselves as both workable and superior to CODASYL, pushing IBM to develop a true production version of System R, known as SQL/DS, and, later, Database 2 (DB2).
"Larry Ellison's Oracle started from a different chain, based on IBM's papers on System R, and beat IBM to market when the first version was released in 1978.["citation needed]
Stonebraker went on to apply the lessons from INGRES to develop a new database, Postgres, which is now known as PostgreSQL. PostgreSQL is often used for global mission critical applications (the .org and .info domain name registries use it as their primary "data store, as do many large companies and financial institutions).
In Sweden, Codd's paper was also read and "Mimer SQL was developed from the mid-1970s at "Uppsala University. In 1984, this project was consolidated into an independent enterprise. In the early 1980s, Mimer introduced transaction handling for high robustness in applications, an idea that was subsequently implemented on most other DBMSs.
Another data model, the "entity–relationship model, emerged in 1976 and gained popularity for "database design as it emphasized a more familiar description than the earlier relational model. Later on, entity–relationship constructs were retrofitted as a data modeling construct for the relational model, and the difference between the two have become irrelevant.["citation needed]
1980s, on the desktop
The 1980s ushered in the age of "desktop computing. The new computers empowered their users with spreadsheets like "Lotus 1-2-3 and database software like "dBASE. The dBASE product was lightweight and easy for any computer user to understand out of the box. "C. Wayne Ratliff the creator of dBASE stated: "dBASE was different from programs like BASIC, C, FORTRAN, and COBOL in that a lot of the dirty work had already been done. The data manipulation is done by dBASE instead of by the user, so the user can concentrate on what he is doing, rather than having to mess with the dirty details of opening, reading, and closing files, and managing space allocation." dBASE was one of the top selling software titles in the 1980s and early 1990s.
The 1990s, along with a rise in "object-oriented programming, saw a growth in how data in various databases were handled. Programmers and designers began to treat the data in their databases as objects. That is to say that if a person's data were in a database, that person's attributes, such as their address, phone number, and age, were now considered to belong to that person instead of being extraneous data. This allows for relations between data to be relations to objects and their attributes and not to individual fields. The term ""object-relational impedance mismatch" described the inconvenience of translating between programmed objects and database tables. "Object databases and "object-relational databases attempt to solve this problem by providing an object-oriented language (sometimes as extensions to SQL) that programmers can use as alternative to purely relational SQL. On the programming side, libraries known as "object-relational mappings (ORMs) attempt to solve the same problem.
2000s, NoSQL and NewSQL
"XML databases are a type of structured document-oriented database that allows querying based on "XML document attributes. XML databases are mostly used in "enterprise database management, where XML is being used as the machine-to-machine data interoperability standard. XML database management systems include "commercial software "MarkLogic and "Oracle Berkeley DB XML, and a free use software "Clusterpoint Distributed XML/JSON Database. All are "enterprise software database platforms and support industry standard "ACID-compliant "transaction processing with strong database consistency characteristics and high level of database security.
NoSQL databases are often very fast, do not require fixed table schemas, avoid join operations by storing "denormalized data, and are designed to "scale horizontally. The most popular NoSQL systems include "MongoDB, "Couchbase, "Riak, "Memcached, "Redis, "CouchDB, "Hazelcast, "Apache Cassandra, and "HBase, which are all "open-source software products.
In recent years, there was a high demand for massively distributed databases with high partition tolerance but according to the "CAP theorem it is impossible for a "distributed system to simultaneously provide "consistency, availability, and partition tolerance guarantees. A distributed system can satisfy any two of these guarantees at the same time, but not all three. For that reason, many NoSQL databases are using what is called "eventual consistency to provide both availability and partition tolerance guarantees with a reduced level of data consistency.
NewSQL is a class of modern relational databases that aims to provide the same scalable performance of NoSQL systems for online transaction processing (read-write) workloads while still using SQL and maintaining the ACID guarantees of a traditional database system. Such databases include "ScaleBase, "Clustrix, "EnterpriseDB, "MemSQL, "NuoDB, and "VoltDB.
Database technology has been an active research topic since the 1960s, both in "academia and in the research and development groups of companies (for example "IBM Research). Research activity includes "theory and development of "prototypes. Notable research topics have included "models, the atomic transaction concept, and related "concurrency control techniques, query languages and "query optimization methods, "RAID, and more.
The database research area has several dedicated "academic journals (for example, "ACM Transactions on Database Systems-TODS, "Data and Knowledge Engineering-DKE) and annual "conferences (e.g., "ACM "SIGMOD, ACM "PODS, "VLDB, "IEEE ICDE).
One way to classify databases involves the type of their contents, for example: "bibliographic, document-text, statistical, or multimedia objects. Another way is by their application area, for example: accounting, music compositions, movies, banking, manufacturing, or insurance. A third way is by some technical aspect, such as the database structure or interface type. This section lists a few of the adjectives used to characterize different kinds of databases.
- An "in-memory database is a database that primarily resides in "main memory, but is typically backed-up by non-volatile computer data storage. Main memory databases are faster than disk databases, and so are often used where response time is critical, such as in telecommunications network equipment. "SAP HANA platform is a very hot topic for in-memory database. By May 2012, HANA was able to run on servers with 100TB main memory powered by IBM. The co founder of the company claimed that the system was big enough to run the 8 largest SAP customers.
- An "active database includes an event-driven architecture which can respond to conditions both inside and outside the database. Possible uses include security monitoring, alerting, statistics gathering and authorization. Many databases provide active database features in the form of "database triggers.
- A "cloud database relies on "cloud technology. Both the database and most of its DBMS reside remotely, "in the cloud", while its applications are both developed by programmers and later maintained and utilized by (application's) end-users through a "web browser and "Open APIs.
- "Data warehouses archive data from operational databases and often from external sources such as market research firms. The warehouse becomes the central source of data for use by managers and other end-users who may not have access to operational data. For example, sales data might be aggregated to weekly totals and converted from internal product codes to use "UPCs so that they can be compared with "ACNielsen data. Some basic and essential components of data warehousing include extracting, analyzing, and "mining data, transforming, loading, and managing data so as to make them available for further use.
- A "deductive database combines "logic programming with a relational database, for example by using the "Datalog language.
- A "distributed database is one in which both the data and the DBMS span multiple computers.
- A document-oriented database is designed for storing, retrieving, and managing document-oriented, or semi structured data, information. Document-oriented databases are one of the main categories of NoSQL databases.
- An "embedded database system is a DBMS which is tightly integrated with an application software that requires access to stored data in such a way that the DBMS is hidden from the application's end-users and requires little or no ongoing maintenance.
- End-user databases consist of data developed by individual end-users. Examples of these are collections of documents, spreadsheets, presentations, multimedia, and other files. Several products exist to support such databases. Some of them are much simpler than full-fledged DBMSs, with more elementary DBMS functionality.
- A "federated database system comprises several distinct databases, each with its own DBMS. It is handled as a single database by a federated database management system (FDBMS), which transparently integrates multiple autonomous DBMSs, possibly of different types (in which case it would also be a "heterogeneous database system), and provides them with an integrated conceptual view.
- Sometimes the term multi-database is used as a synonym to federated database, though it may refer to a less integrated (e.g., without an FDBMS and a managed integrated schema) group of databases that cooperate in a single application. In this case, typically "middleware is used for distribution, which typically includes an atomic commit protocol (ACP), e.g., the "two-phase commit protocol, to allow "distributed (global) transactions across the participating databases.
- A "graph database is a kind of NoSQL database that uses "graph structures with nodes, edges, and properties to represent and store information. General graph databases that can store any graph are distinct from specialized graph databases such as "triplestores and "network databases.
- An "array DBMS is a kind of NoSQL DBMS that allows to model, store, and retrieve (usually large) multi-dimensional "arrays such as satellite images and climate simulation output.
- In a "hypertext or "hypermedia database, any word or a piece of text representing an object, e.g., another piece of text, an article, a picture, or a film, can be "hyperlinked to that object. Hypertext databases are particularly useful for organizing large amounts of disparate information. For example, they are useful for organizing "online encyclopedias, where users can conveniently jump around the text. The "World Wide Web is thus a large distributed hypertext database.
- A "knowledge base (abbreviated KB, kb or Δ) is a special kind of database for "knowledge management, providing the means for the computerized collection, organization, and "retrieval of "knowledge. Also a collection of data representing problems with their solutions and related experiences.
- A "mobile database can be carried on or synchronized from a mobile computing device.
- "Operational databases store detailed data about the operations of an organization. They typically process relatively high volumes of updates using "transactions. Examples include "customer databases that record contact, credit, and demographic information about a business' customers, personnel databases that hold information such as salary, benefits, skills data about employees, "enterprise resource planning systems that record details about product components, parts inventory, and financial databases that keep track of the organization's money, accounting and financial dealings.
- A "parallel database seeks to improve performance through "parallelization for tasks such as loading data, building indexes and evaluating queries.
- The major parallel DBMS architectures which are induced by the underlying "hardware architecture are:
- "Shared memory architecture, where multiple processors share the main memory space, as well as other data storage.
- Shared disk architecture, where each processing unit (typically consisting of multiple processors) has its own main memory, but all units share the other storage.
- "Shared nothing architecture, where each processing unit has its own main memory and other storage.
- The major parallel DBMS architectures which are induced by the underlying "hardware architecture are:
- "Probabilistic databases employ "fuzzy logic to draw inferences from imprecise data.
- "Real-time databases process transactions fast enough for the result to come back and be acted on right away.
- A "spatial database can store the data with multidimensional features. The queries on such data include location-based queries, like "Where is the closest hotel in my area?".
- A "temporal database has built-in time aspects, for example a temporal data model and a temporal version of SQL. More specifically the temporal aspects usually include valid-time and transaction-time.
- A "terminology-oriented database builds upon an "object-oriented database, often customized for a specific field.
- An "unstructured data database is intended to store in a manageable and protected way diverse objects that do not fit naturally and conveniently in common databases. It may include email messages, documents, journals, multimedia objects, etc. The name may be misleading since some objects can be highly structured. However, the entire possible object collection does not fit into a predefined structured framework. Most established DBMSs now support unstructured data in various ways, and new dedicated DBMSs are emerging.
Design and modeling
The first task of a database designer is to produce a "conceptual data model that reflects the structure of the information to be held in the database. A common approach to this is to develop an entity-relationship model, often with the aid of drawing tools. Another popular approach is the "Unified Modeling Language. A successful data model will accurately reflect the possible state of the external world being modeled: for example, if people can have more than one phone number, it will allow this information to be captured. Designing a good conceptual data model requires a good understanding of the application domain; it typically involves asking deep questions about the things of interest to an organisation, like "can a customer also be a supplier?", or "if a product is sold with two different forms of packaging, are those the same product or different products?", or "if a plane flies from New York to Dubai via Frankfurt, is that one flight or two (or maybe even three)?". The answers to these questions establish definitions of the terminology used for entities (customers, products, flights, flight segments) and their relationships and attributes.
Producing the conceptual data model sometimes involves input from "business processes, or the analysis of "workflow in the organization. This can help to establish what information is needed in the database, and what can be left out. For example, it can help when deciding whether the database needs to hold historic data as well as current data.
Having produced a conceptual data model that users are happy with, the next stage is to translate this into a "schema that implements the relevant data structures within the database. This process is often called logical database design, and the output is a "logical data model expressed in the form of a schema. Whereas the conceptual data model is (in theory at least) independent of the choice of database technology, the logical data model will be expressed in terms of a particular database model supported by the chosen DBMS. (The terms data model and database model are often used interchangeably, but in this article we use data model for the design of a specific database, and database model for the modelling notation used to express that design.)
The most popular database model for general-purpose databases is the relational model, or more precisely, the relational model as represented by the SQL language. The process of creating a logical database design using this model uses a methodical approach known as "normalization. The goal of normalization is to ensure that each elementary "fact" is only recorded in one place, so that insertions, updates, and deletions automatically maintain consistency.
The final stage of database design is to make the decisions that affect performance, scalability, recovery, security, and the like. This is often called physical database design. A key goal during this stage is "data independence, meaning that the decisions made for performance optimization purposes should be invisible to end-users and applications. There are two types of data independence: Physical data independence and logical data independence. Physical design is driven mainly by performance requirements, and requires a good knowledge of the expected workload and access patterns, and a deep understanding of the features offered by the chosen DBMS.
Another aspect of physical database design is security. It involves both defining "access control to database objects as well as defining security levels and methods for the data itself.
A database model is a type of data model that determines the logical structure of a database and fundamentally determines in which manner "data can be stored, organized, and manipulated. The most popular example of a database model is the relational model (or the SQL approximation of relational), which uses a table-based format.
Common logical data models for databases include:
- "Navigational databases
- "Relational model
- "Entity–relationship model
- "Object model
- "Document model
- "Entity–attribute–value model
- "Star schema
An object-relational database combines the two related structures.
"Physical data models include:
Other models include:
Specialized models are optimized for particular types of data:
External, conceptual, and internal views
A database management system provides three views of the database data:
- The external level defines how each group of end-users sees the organization of data in the database. A single database can have any number of views at the external level.
- The conceptual level unifies the various external views into a compatible global view. It provides the synthesis of all the external views. It is out of the scope of the various database end-users, and is rather of interest to database application developers and database administrators.
- The internal level (or physical level) is the internal organization of data inside a DBMS. It is concerned with cost, performance, scalability and other operational matters. It deals with storage layout of the data, using storage structures such as "indexes to enhance performance. Occasionally it stores data of individual views ("materialized views), computed from generic data, if performance justification exists for such redundancy. It balances all the external views' performance requirements, possibly conflicting, in an attempt to optimize overall performance across all activities.
While there is typically only one conceptual (or logical) and physical (or internal) view of the data, there can be any number of different external views. This allows users to see database information in a more business-related way rather than from a technical, processing viewpoint. For example, a financial department of a company needs the payment details of all employees as part of the company's expenses, but does not need details about employees that are the interest of the "human resources department. Thus different departments need different views of the company's database.
The three-level database architecture relates to the concept of data independence which was one of the major initial driving forces of the relational model. The idea is that changes made at a certain level do not affect the view at a higher level. For example, changes in the internal level do not affect application programs written using conceptual level interfaces, which reduces the impact of making physical changes to improve performance.
The conceptual view provides a level of indirection between internal and external. On one hand it provides a common view of the database, independent of different external view structures, and on the other hand it abstracts away details of how the data are stored or managed (internal level). In principle every level, and even every external view, can be presented by a different data model. In practice usually a given DBMS uses the same data model for both the external and the conceptual levels (e.g., relational model). The internal level, which is hidden inside the DBMS and depends on its implementation, requires a different level of detail and uses its own types of data structure types.
Separating the external, conceptual and internal levels was a major feature of the relational database model implementations that dominate 21st century databases.
Database languages are special-purpose languages, which do one or more of the following:
- "Data definition language – defines data types such as creating, altering, or dropping and the relationships among them
- "Data manipulation language – performs tasks such as inserting, updating, or deleting data occurrences
- "Query language – allows searching for information and computing derived information
Database languages are specific to a particular data model.Notable examples include:
- SQL combines the roles of data definition, data manipulation, and query in a single language. It was one of the first commercial languages for the relational model, although it departs in some respects from "the relational model as described by Codd (for example, the rows and columns of a table can be ordered). SQL became a standard of the "American National Standards Institute (ANSI) in 1986, and of the "International Organization for Standardization (ISO) in 1987. The standards have been regularly enhanced since and is supported (with varying degrees of conformance) by all mainstream commercial relational DBMSs.
- "OQL is an object model language standard (from the "Object Data Management Group). It has influenced the design of some of the newer query languages like JDOQL and "EJB QL.
- "XQuery is a standard XML query language implemented by XML database systems such as "MarkLogic and "eXist, by relational databases with XML capability such as Oracle and DB2, and also by in-memory XML processors such as "Saxon.
- "SQL/XML combines "XQuery with SQL.
A database language may also incorporate features like:
- DBMS-specific Configuration and storage engine management
- Computations to modify query results, like counting, summing, averaging, sorting, grouping, and cross-referencing
- Constraint enforcement (e.g. in an automotive database, only allowing one engine type per car)
- Application programming interface version of the query language, for programmer convenience
Performance, security, and availability
Because of the critical importance of database technology to the smooth running of an enterprise, database systems include complex mechanisms to deliver the required performance, security, and availability, and allow database administrators to control the use of these features.
Database storage is the container of the physical materialization of a database. It comprises the internal (physical) level in the database architecture. It also contains all the information needed (e.g., "metadata, "data about the data", and internal "data structures) to reconstruct the conceptual level and external level from the internal level when needed. Putting data into permanent storage is generally the responsibility of the "database engine a.k.a. "storage engine". Though typically accessed by a DBMS through the underlying operating system (and often utilizing the operating systems' "file systems as intermediates for storage layout), storage properties and configuration setting are extremely important for the efficient operation of the DBMS, and thus are closely maintained by database administrators. A DBMS, while in operation, always has its database residing in several types of storage (e.g., memory and external storage). The database data and the additional needed information, possibly in very large amounts, are coded into bits. Data typically reside in the storage in structures that look completely different from the way the data look in the conceptual and external levels, but in ways that attempt to optimize (the best possible) these levels' reconstruction when needed by users and programs, as well as for computing additional types of needed information from the data (e.g., when querying the database).
Some DBMSs support specifying which "character encoding was used to store data, so multiple encodings can be used in the same database.
Various low-level "database storage structures are used by the storage engine to serialize the data model so it can be written to the medium of choice. Techniques such as indexing may be used to improve performance. Conventional storage is row-oriented, but there are also "column-oriented and "correlation databases.
Often storage redundancy is employed to increase performance. A common example is storing materialized views, which consist of frequently needed external views or query results. Storing such views saves the expensive computing of them each time they are needed. The downsides of materialized views are the overhead incurred when updating them to keep them synchronized with their original updated database data, and the cost of storage redundancy.
Occasionally a database employs storage redundancy by database objects replication (with one or more copies) to increase data availability (both to improve performance of simultaneous multiple end-user accesses to a same database object, and to provide resiliency in a case of partial failure of a distributed database). Updates of a replicated object need to be synchronized across the object copies. In many cases, the entire database is replicated.
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"Database security deals with all various aspects of protecting the database content, its owners, and its users. It ranges from protection from intentional unauthorized database uses to unintentional database accesses by unauthorized entities (e.g., a person or a computer program).
Database access control deals with controlling who (a person or a certain computer program) is allowed to access what information in the database. The information may comprise specific database objects (e.g., record types, specific records, data structures), certain computations over certain objects (e.g., query types, or specific queries), or utilizing specific access paths to the former (e.g., using specific indexes or other data structures to access information). Database access controls are set by special authorized (by the database owner) personnel that uses dedicated protected security DBMS interfaces.
This may be managed directly on an individual basis, or by the assignment of individuals and "privileges to groups, or (in the most elaborate models) through the assignment of individuals and groups to roles which are then granted entitlements. Data security prevents unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or subsets of it called "subschemas". For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data. If the DBMS provides a way to interactively enter and update the database, as well as interrogate it, this capability allows for managing personal databases.
"Data security in general deals with protecting specific chunks of data, both physically (i.e., from corruption, or destruction, or removal; e.g., see "physical security), or the interpretation of them, or parts of them to meaningful information (e.g., by looking at the strings of bits that they comprise, concluding specific valid credit-card numbers; e.g., see "data encryption).
Change and access logging records who accessed which attributes, what was changed, and when it was changed. Logging services allow for a forensic "database audit later by keeping a record of access occurrences and changes. Sometimes application-level code is used to record changes rather than leaving this to the database. Monitoring can be set up to attempt to detect security breaches.
Transactions and concurrency
"Database transactions can be used to introduce some level of "fault tolerance and "data integrity after recovery from a "crash. A database transaction is a unit of work, typically encapsulating a number of operations over a database (e.g., reading a database object, writing, acquiring "lock, etc.), an abstraction supported in database and also other systems. Each transaction has well defined boundaries in terms of which program/code executions are included in that transaction (determined by the transaction's programmer via special transaction commands).
The acronym "ACID describes some ideal properties of a database transaction: "Atomicity, "Consistency, "Isolation, and "Durability.
A database built with one DBMS is not portable to another DBMS (i.e., the other DBMS cannot run it). However, in some situations, it is desirable to move, migrate a database from one DBMS to another. The reasons are primarily economical (different DBMSs may have different "total costs of ownership or TCOs), functional, and operational (different DBMSs may have different capabilities). The migration involves the database's transformation from one DBMS type to another. The transformation should maintain (if possible) the database related application (i.e., all related application programs) intact. Thus, the database's conceptual and external architectural levels should be maintained in the transformation. It may be desired that also some aspects of the architecture internal level are maintained. A complex or large database migration may be a complicated and costly (one-time) project by itself, which should be factored into the decision to migrate. This in spite of the fact that tools may exist to help migration between specific DBMSs. Typically, a DBMS vendor provides tools to help importing databases from other popular DBMSs.
Building, maintaining, and tuning
After designing a database for an application, the next stage is building the database. Typically, an appropriate "general-purpose DBMS can be selected to be utilized for this purpose. A DBMS provides the needed "user interfaces to be utilized by database administrators to define the needed application's data structures within the DBMS's respective data model. Other user interfaces are used to select needed DBMS parameters (like security related, storage allocation parameters, etc.).
When the database is ready (all its data structures and other needed components are defined), it is typically populated with initial application's data (database initialization, which is typically a distinct project; in many cases using specialized DBMS interfaces that support bulk insertion) before making it operational. In some cases, the database becomes operational while empty of application data, and data are accumulated during its operation.
After the database is created, initialised and populated it needs to be maintained. Various database parameters may need changing and the database may need to be tuned ("tuning) for better performance; application's data structures may be changed or added, new related application programs may be written to add to the application's functionality, etc.
Backup and restore
Sometimes it is desired to bring a database back to a previous state (for many reasons, e.g., cases when the database is found corrupted due to a software error, or if it has been updated with erroneous data). To achieve this, a backup operation is done occasionally or continuously, where each desired database state (i.e., the values of its data and their embedding in database's data structures) is kept within dedicated backup files (many techniques exist to do this effectively). When this state is needed, i.e., when it is decided by a database administrator to bring the database back to this state (e.g., by specifying this state by a desired point in time when the database was in this state), these files are utilized to restore that state.
Static analysis techniques for software verification can be applied also in the scenario of query languages. In particular, the *"Abstract interpretation framework has been extended to the field of query languages for relational databases as a way to support sound approximation techniques. The semantics of query languages can be tuned according to suitable abstractions of the concrete domain of data. The abstraction of relational database system has many interesting applications, in particular, for security purposes, such as fine grained access control, watermarking, etc.
Other DBMS features might include:
- "Database logs
- Graphics component for producing graphs and charts, especially in a data warehouse system
- "Query optimizer – Performs "query optimization on every query to choose an efficient "query plan (a partial order (tree) of operations) to be executed to compute the query result. May be specific to a particular storage engine.
- Tools or hooks for database design, application programming, application program maintenance, database performance analysis and monitoring, database configuration monitoring, DBMS hardware configuration (a DBMS and related database may span computers, networks, and storage units) and related database mapping (especially for a distributed DBMS), storage allocation and database layout monitoring, storage migration, etc.
- Increasingly, there are calls for a single system that incorporates all of these core functionalities into the same build, test, and deployment framework for database management and source control. Borrowing from other developments in the software industry, some market such offerings as ""DevOps for database".
- "Comparison of database tools
- "Comparison of object database management systems
- "Comparison of object-relational database management systems
- "Comparison of relational database management systems
- "Data hierarchy
- "Data bank
- "Data store
- "Database theory
- "Database testing
- "Database-centric architecture
- "Journal of Database Management
- "Question-focused dataset
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