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Database Management Systems

… help create, define, host, and manage databases. Various kinds of DBMS were designed over time, such as file-based, Relational DBMS (RDBMS), NoSQL, Graph based, and Key/Value stores.

DBMSs

Some essential features of a DBMS include:

FeatureDescription
Concurrencya real world application might have multiple users interacting with it simultaneously; a DBMS makes sure that these concurrent interactions succeed without corrupting or losing any data
Consistencywith so many concurrent interactions, the DBMS needs to ensure that the data remains consistent and valid throughout the database
SecurityDBMS provide fine-grained security controls through user authentication and permissions; this will prevent unauthorized viewing or editing of sensitive data
Reliabilityit is easy to backup databases and rolls them back to a previous state in case of data loss or a breach
Structured Query LanguageSQL simplifies user interaction with the database with an intuitive syntax supporting various operations

Architecture

flowchart LR

A[User]
B[Tier I]
C[Tier II]
D[DBMS]
E[Users]
F[Database Administrator]

A --> B
B --> C
C --> D
D --> E
D --> F

Tier I usually consists of client-side applications such as websites or GUI programs. These applications consist of high-level interactions such as user login or commenting. The data from these interactions is passed to Tier II through API calls or requests.

Relational Databases

… uses a schema, a template, to dictate the data structure stored in the database. Tables in relational databases are associated with keys that provide a quick database summary or access to the specific row or column when specific data needs to be reviewed. These tables, also called entities, are all related to each other. The concept required to link one table to another using its keys, is called a relational database management system (RDBMS).

erDiagram
    CUSTOMER {
        string customer_id
        string name
        string address
        string contact_info
    }
    PRODUCT {
        string product_id
        string product_name
        string product_description
    }
    ORDER {
        string order_id
        string customer_id
        string product_id
        int quantity
    }

    CUSTOMER ||--o| ORDER: has
    PRODUCT ||--o| ORDER: contains

Non-relational Databases

… also called a NoSQL database, does not use tables, rows, and columns or primary keys, relationships, or schemas. Instead, a NoSQL database stores data using various storage models, depending on the type of data stored. Four common storage models are:

  • Key-Value
  • Document-Based
  • Wide-Column
  • Graph
classDiagram
    class Post1 {
        ID: "100001"
        date: "01-01-2021"
        content: "Welcome to this web application."
    }

    class Post2 {
        ID: "100002"
        date: "02-01-2021"
        content: "This is the first post on this web app."
    }

    class Post3 {
        ID: "100003"
        date: "02-01-2021"
        content: "Reminder: Tomorrow is the ..."
    }

The above example can be represented using JSON as:

{
  "100001": {
    "date": "01-01-2021",
    "content": "Welcome to this web application."
  },
  "100002": {
    "date": "02-01-2021",
    "content": "This is the first post on this web app."
  },
  "100003": {
    "date": "02-01-2021",
    "content": "Reminder: Tomorrow is the ..."
  }
}