Blog om databaser

sop using github

The acces to github is through the github website and locally on your machine, through a commandline and local git commands. Once these are configurede, you are ready to go. Without revealing my deatiled insight I can tell that GIT is a distributed version control system that allows multible repositories to be synchronized. Most version control system have a central repository and merging repositories is an elaborate task. GIT as such have some of the same conflict resolution issues, but handling these issues is much more common place as GIT…

Om SQL environments. Environments, Catalogs, Clusters, Schemas.

DA Den grundlæggende notation for en samling af tabeller, view, index der implementerer referentiel intergritet, triggere og funtioner, procedurer og pakker pÃ¥ relationelle databaser er schemaer eller pÃ¥ dansk, skemaer. Et katalog, er et antal skemaer, samt et information_schema eller et system_skema som indeholder skemainformation. I en relationel database er alle skemainformationer i sig selv data som er forankret i et systemskema. Opslag pÃ¥ systemets tilstand og definitionen pÃ¥ de enkelte database defininitioner er i sig selv data i systemskemaet. NÃ¥r en tabels struktur skal undersøges laves et opslag pÃ¥…

Data Manipulation Language (DML)

Data Manipulation Language (DML) [Fotache 2013]. EN: A relational database has a special language to perform SQL (SELECT, INSERT, UPDATE, DELETE) and extended SQL (grouping functions, stored procedures, triggers). This special language is called data manipulation language (DML). DA: Forespørgselssprog mod databasen – SQL (SELECT, INSERT, UPDATE, DELETE). DML udføres af SQL-fortolkeren og kan indgå i en transaktion. Når en transaktion startes kan alle ændringer på databasen enten committes som en enhed eller rulles tilbage og efterlade databasen i en uændret tilstand.

Data Definition Language (DDL)

Data Definition Language (DDL) [Fotache 2013] EN: In a relational database the creation and modification of schemaelements is don through a interpreted data definition language(). DDL statements commit, that is, DDL statements cannot be part of a transaction. Then starting a transaction every SQL statement following will be in its own state until the transaction is committed or rolled back. A DLL statement would break the transaction by committing the current state and statement. DA: Definitionssprog. Oprettelse af tabeller, view, fremmednøgler, indeks. I en relationel database findes der et specielt…

View

View. …We define a view to be the set of caches of which a particular client is aware. … A client uses a consistent hash function to map a object to one of the caches in its view. …[Karger 1997] DA: I consistent hashing er det cachen der er redundant og opslag sker pÃ¥ en lokal ‘virtuel’-cache. Det reducerer belastningen pÃ¥ den maskine som er master for dokumentetet. Den enkelte maskine forhandler sÃ¥ adgang til et sæt virtuel caches afhængig af geografisk lokation, ip nummer eller andet. Det tilgængelige sæt af caches…