Oracle Definitions
Version 21c

General Information
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Too often keywords are used that have different meanings in different products or definitions that are contrary to general usage. As I locate misunderstandings I will try to link from various Library pages to this page and provide short, succinct, definitions and examples.

If you have something you don't understand and would like added to this page, sorry but it must be Oracle database related not about your parents, children, spouse, or the sorry state of humanity ... send them to me and I'll try to put something together and post it here.
Block This word has many different, unrelated, meanings in different products and contexts within the Oracle family of products. A database block, roughly equivalent to a "page" in SQL Server. A database block is the smallest unit of logical space allocation within a tablespace datafile. A block can also refer to a PL/SQL block which is a series of commands with a "block" of code that starts with the word "BEGIN" and completes with the word "END".
Container Oracle has from time-to-time totally mangled their use of keywords and it appears "container" is the new "block." What a mess. Forget Oracle's docs ... they were written by someone that knows what the word is supposed to mean and thus doesn't understand the near infinite confusion the description will generate. Here is, in the common vernacular, what the word actually means ... "Everything is a container in a container database. CDB$ROOT is a container ... PDB$SEED is a container ... every pluggable database whether plugged into a container database or just sitting on "disk" is a container. The only thing that is not a "container" is the container that holds all of the containers ... that they call a CDB: "Container Database" just to make sure they slow down adoption of what is otherwise a great technology.

Can you tell I am really unhappy with the docs not the product? I hope so.
Cluster This word has many different, unrelated, meanings in different products owned by different companies, for example the definition in the Oracle database is different from the definition in SQL Server and word, even in the context of the Oracle Database can have multiple meanings. For example I might use "Cluster" to refer to an operating system cluster, to a Real Applications (RAC) cluster, or to a way of placing multiple segments into the same block as in, for example, a Sorted Hash Cluster. If you hear the word cluster you need to understand the context and the product to understand what is meant.
Database A totally meaningless word lacking any context in Oracle with the release of the 12c container architecture. It is recommended that it no longer be used for anything other than a discussion over cognac of the so-called "good old days."
EDS Extended Datatype Support ... refers to support for non-standard data types as in Logical Standby and Streams replication
FGA Fine Grained Auditing ... a reference to the DBMS_FGA package
Heap Table A table containing an unsorted "heap" of data. All default tables, in all major commercial relational database products, are heap table. Tables that sort data, for example Index Organized Tables, are not heap tables.
PDB Stands for Pluggable DataBase which essentially means an Oracle database plugged into, and inheriting, its metadata, PL/SQL objects, Java objects, and libraries from a CDB$ROOT container.
RLS Row Level Security ... a reference to the DBMS_RLS package
Scalar Subquery A subquery that returns exactly one value value or NULL. For example: SELECT dummy FROM dual;

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Kernel Subsystems
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