Search results
Results from the WOW.Com Content Network
A data control language (DCL) is a syntax similar to a computer programming language used to control access to data stored in a database (authorization). In particular, it is a component of Structured Query Language (SQL). Data Control Language is one of the logical group in SQL Commands.
Multiversion concurrency control (MCC or MVCC), is a non-locking concurrency control method commonly used by database management systems to provide concurrent access to the database and in programming languages to implement transactional memory. [1]
Attributes can be data, user, session or tools based to deliver the greatest level of flexibility in dynamically granting/denying access to a specific data element. On big data , and distributed file systems such as Hadoop, ABAC applied at the data layer control access to folder, sub-folder, file, sub-file and other granular.
Thus concurrency control is an essential element for correctness in any system where two database transactions or more, executed with time overlap, can access the same data, e.g., virtually in any general-purpose database system. Consequently, a vast body of related research has been accumulated since database systems emerged in the early 1970s.
A precedence graph, also named conflict graph [1] and serializability graph, is used in the context of concurrency control in databases. [2] It is the directed graph representing precedence of transactions in the schedule, as reflected by precedence of conflicting operations in the transactions.
Sometimes a transaction control language (TCL) [1] is argued to be part of the sub-language set as well. DQL statements are used for performing queries on the data within schema objects. The purpose of DQL commands is to get the schema relation based on the query passed to it.
Query by Example (QBE) is a database query language for relational databases. It was devised by Moshé M. Zloof at IBM Research during the mid-1970s, in parallel to the development of SQL . [ 1 ] It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions.
Optimistic concurrency control transactions involve these phases: [2] Begin: Record a timestamp marking the transaction's beginning. Modify: Read database values, and tentatively write changes. Validate: Check whether other transactions have modified data that this transaction has used (read or written). This includes transactions that ...