An information system is a formal system for storing and processing information. An information system could be a set of cardboard boxes containing manila folders along with rules for how to store and retrieve the folders. However, most companies today use a database to automate their information systems. A database is an organized collection of information treated as a unit. The purpose of a database is to collect, store, and retrieve related information for use by database applications.
The preceding database management systems stored data in rigid, predetermined relationships. Because no data definition language existed, changing the structure of the data was difficult. Also, these systems lacked a simple query language, which hindered application development.
1z0 051 Oracle Database Sql Fundamentals I Free Download
tag_hash_104 🔥 https://urlin.us/2yjYh3 🔥
In his seminal 1970 paper "A Relational Model of Data for Large Shared Data Banks," E. F. Codd defined a relational model based on mathematical set theory. Today, the most widely accepted database model is the relational model.
A table is a two-dimensional representation of a relation in the form of rows (tuples) and columns (attributes). Each row in a table has the same set of columns. A relational database is a database that stores data in relations (tables). For example, a relational database could store information about company employees in an employee table, a department table, and a salary table.
In this case, the RDBMS determines how things should be done and carries out the operation. For example, after an application queries a table, the database may use an index to find the requested rows, read the data into memory, and perform many other steps before returning a result to the user. The RDBMS stores and retrieves data so that physical operations are transparent to database applications.
Oracle Database is an RDBMS. An RDBMS that implements object-oriented features such as user-defined types, inheritance, and polymorphism is called an object-relational database management system (ORDBMS). Oracle Database has extended the relational model to an object-relational model, making it possible to store complex business models in a relational database.
Oracle Version 3, released in 1983, was the first relational database to run on mainframes, minicomputers, and personal computers. The database was written in C, enabling the database to be ported to multiple platforms.
Version 4 introduced multiversion read consistency. Version 5, released in 1985, supported client/server computing and distributed database systems. Version 6 brought enhancements to disk I/O, row locking, scalability, and backup and recovery. Also, Version 6 introduced the first version of the PL/SQL language, a proprietary procedural extension to SQL.
Oracle8i Database, released in 1999, provided native support for internet protocols and server-side support for Java. Oracle8i was designed for internet computing, enabling the database to be deployed in a multitier environment.
Oracle9i Database introduced Oracle RAC in 2001, enabling multiple instances to access a single database simultaneously. Additionally, Oracle XML Database (Oracle XML DB) introduced the ability to store and query XML.
Oracle Database 10g introduced grid computing in 2003. This release enabled organizations to virtualize computing resources by building a grid infrastructure based on low-cost commodity servers. A key goal was to make the database self-managing and self-tuning. Oracle Automatic Storage Management (Oracle ASM) helped achieve this goal by virtualizing and simplifying database storage management.
SQL is the ANSI standard language for relational databases. All operations on the data in an Oracle database are performed using SQL statements. For example, you use SQL to create tables and query and modify data in tables.
A primary benefit of PL/SQL is the ability to store application logic in the database itself. A PL/SQL procedure or function is a schema object that consists of a set of SQL statements and other PL/SQL constructs, grouped together, stored in the database, and run as a unit to solve a specific problem or to perform a set of related tasks. The principal benefit of server-side programming is that built-in functionality can be deployed anywhere.
Oracle Database can also store program units written in Java. A Java stored procedure is a Java method published to SQL and stored in the database for general use. You can call existing PL/SQL programs from Java and Java programs from PL/SQL.
Transactions are one feature that set Oracle Database apart from a file system. If you perform an atomic operation that updates several files, and if the system fails halfway through, then the files will not be consistent. In contrast, a transaction moves an Oracle database from one consistent state to another. The basic principle of a transaction is "all or nothing": an atomic operation succeeds or fails as a whole.
The database can also provide read consistency to all queries in a transaction, known as transaction-level read consistency. In this case, each statement in a transaction sees data from the same point in time, which is the time at which the transaction began.
In general, a server reliably manages a large amount of data in a multiuser environment so that users can concurrently access the same data. A database server also prevents unauthorized access and provides efficient solutions for failure recovery.
Because an instance and a database are so closely connected, the term Oracle database is sometimes used to refer to both instance and database. In the strictest sense the terms have the following meanings:
An instance is a set of memory structures that manage database files. The instance consists of a shared memory area, called the system global area (SGA), and a set of background processes. An instance can exist independently of database files.
The following figure shows a database and its instance. For each user connection to the instance, a client process runs the application. Each client process is associated with its own server process. The server process has its own private session memory, known as the program global area (PGA).
Although in the strict sense an Oracle database is a set of physical structures (files and memory structures), applications can interact with multiple logical databases inside a single physical database, or a single logical database distributed across multiple physical databases.
A non-CDB is a traditional Oracle database that cannot contain PDBs. A CDB is a single physical database that contains zero, one, or many user-created pluggable databases. A pluggable database (PDB) is a portable collection of schemas, schema objects, and nonschema objects that appears to an Oracle Net client as a non-CDB.
Large enterprises may use hundreds or thousands of databases, often running on different platforms on multiple physical servers. Modern servers are able to handle heavier workloads than before. A database may use only a fraction of the server hardware capacity. This approach wastes both hardware and human resources.
Starting in Oracle Database 12c, you must create a database as either a CDB or non-CDB. You can plug a traditional non-CDB into a CDB as a PDB. The PDB/non-CDB compatibility guarantee means that a PDB behaves the same as a non-CDB as seen from a client connecting with Oracle Net.
The following figure shows two separate non-CDBs: hr and sales. Each non-CDB has its own memory and set of database files, and resides on its own computer. Each non-CDB has its own dedicated user application.
Physically, MYCDB is an Oracle database. MYCDB has one database instance, although multiple instances are possible in Oracle Real Application Clusters, and one set of database files, just like a non-CDB.
MYCDB contains two PDBs: hrpdb and salespdb. As shown in Figure 1-3, these PDBs appear to their respective applications just as they did before database consolidation. To administer the CDB itself or any PDB within it, a CDB administrator can connect to the CDB root, which is a collection of schemas, schema objects, and nonschema objects to which all PDBs belong.
In a sharding architecture, each database is hosted on a dedicated server with its own local resources - CPU, memory, flash, or disk. Each database in such configuration is called a shard. All of the shards together make up a single logical database, which is referred to as a sharded database.
Horizontal partitioning involves splitting a database table across shards so that each shard contains the table with the same columns but a different subset of rows. A table split up in this manner is also known as a sharded table.
A use case is distributing customer account data across multiple physical databases. For example, a customer with ID 28459361 may look up his records. The following figure shows a possible architecture. The customer request is routed through a connection pool, where sharding directors (network listeners) direct the request to the appropriate shard, which contains all the customer rows.
Physical data is data viewable at the operating system level. For example, operating system utilities such as the Linux ls and ps can list database files and processes. Logical data such as a table is meaningful only for the database. A SQL statement can list the tables in an Oracle database, but an operating system utility cannot.
The database has physical structures and logical structures. Because the physical and logical structures are separate, you can manage the physical storage of data without affecting access to logical storage structures. For example, renaming a physical database file does not rename the tables whose data is stored in this file.
Every Oracle database has one or more physical data files, which contain all the database data. The data of logical database structures, such as tables and indexes, is physically stored in the data files.
Every Oracle database has a control file. A control file contains metadata specifying the physical structure of the database, including the database name and the names and locations of the database files. 0852c4b9a8
mr bean movie 2011 free download
free download galli cricket games