Notes for BSc CSIT

  Thread is different from the task in the following ways:- A t ask  describes a program that may need input files and generate output files as a result of its execution and applications are a collection of tasks. Tasks are submitted for execution, and their Output data is gathered at the conclusion. The way tasks are produced, the sequence in which they are executed, and whether they need data interchange to distinguish the application models that come under the task programming umbrella.  A Task may be used to indicate what you want to perform, and then that Task may be attached to a Thread. Threads are utilized to finish the task by splitting it up into pieces and executing them individually in a distributed system. A  thread  is a fundamental unit of CPU utilization that consists of a program counter, a stack, and a collection of registers. Threads have their program and memory areas. A thread of execution is the shortest series of programmed instructions th...

  HYPERVISOR A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems.  The term hypervisor is a variant of supervisor, a traditional term for the kernel of an operating system: the hypervisor is the supervisor of the supervisors, with hyper- used as a stronger variant of super. A hypervisor is a function that abstracts, or separates, operating systems and applications from the underlying computer hardware. This abstraction enables the underlying host machine hardware to run one or more virtual machines as guests independently, allowing numerous guest VMs to effectively shar...

 Cloud Computing Cloud Computing is the delivery of on-demand IT resources (such as the Internet, database, Server, Big-Data, etc ) implemented on the internet to process, manage and store data. In cloud computing, we can pay for only those resources which we have used. Benefits of Cloud Computing: Data backup and Storage of data Powerful server capabilities Incremental Productivity Cost-effective and Time-saving Agility (Access to a broad range of technology) Elasticity    The differentiating public cloud from the private cloud. Public Cloud :  The cloud services which are exposed to the public and can be used by anyone are called public clouds. The public cloud is owned, managed, and operated by businesses, universities, and government organizations. In the public cloud, data centers are located anywhere on the internet.  P rivate Cloud: The cloud services which are private in the internal network within the organizations and selected users ins...

  CLOUD SERVICE REQUIREMENTS 1. Efficiency/cost reduction By using cloud infrastructure, you don’t have to spend huge amounts of money on purchasing and maintaining equipment. 2. Data security Cloud offers many advanced security features that guarantee that data is securely stored and handled. Cloud storage providers implement baseline protections for their platforms and the data they process, such as authentication, access control, and encryption. 3. Scalability Different companies have different IT needs — a large enterprise of 1000+ employees won’t have the same IT requirements as a start-up. Using the cloud is a great solution because it enables enterprises to efficiently — and quickly — scale up/down according to business demands. 4. Mobility Cloud computing allows mobile access to corporate data via smartphones and devices, which is a great way to ensure that no one is ever left out of the loop. Staff with busy schedules, or who live a long way away from the corporat...

 MapReduce  MapReduce is triggered by the map and reduces operations in functional languages, such as Lisp. This model abstracts computation problems through two functions: map and reduce. All problems formulated in this way can be parallelized automatically. All data processed by MapReduce are in the form of key/value pairs. The execution happens in two phases. In the first phase, a map function is invoked once for each input key/value pair and it can generate output key/value pairs as intermediate results. In the second one, all the intermediate results are merged and grouped by keys. The reduce function is called once for each key with associated values and produces output values as the final results. A map function takes a key/value pair as input and produces a list of key/value pairs as output. The type of output key and value can be different from input key and value: map::(key1,value1) => list(key2,value2) A reduce function takes a key and associated value list as in...

  CLOUD SERVICES Cloud computing service models are divided into three categories: Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS) (SaaS). There are evident distinctions between the three in terms of what they can provide a business in terms of storage and resource sharing, but they may also interact with one another to build a single comprehensive cloud computing platform. 1. IaaS (Infrastructure as Service):  This is the most prevalent cloud computing service architecture since it provides the underlying infrastructure of virtual servers, networks, operating systems, and data storage devices. It provides the flexibility, stability, and scalability that many organizations desire from the cloud while eliminating the need for hardware in the office. This makes it excellent for small and medium-sized businesses seeking a cost-effective IT solution to support business growth. IaaS is a completely outsourced pay-for-use service th...

  Cloud The “cloud” in cloud computing can be defined as the set of hardware, networks, storage, services, and interfaces that combine to deliver aspects of computing as a service. Cloud services include the delivery of software, infrastructure, and storage over the Internet. A cloud service is any service made available to users on demand via the Internet from a cloud computing provider's servers as opposed to being provided from a company's own premises servers explained before, the most common cloud service is that one offers data storage disks and virtual servers, i.e. infrastructure. Examples of Infrastructure-as-a-Service (IaaS) companies are Amazon, Rackspace, and Flexi scale. Cloud computing is the use of computing resources (hardware and software) that are delivered as a service over a network (typically the Internet).  Cloud computing is the on-demand availability of computer system resources, especially data storage (cloud storage) and computing power, without direc...

 MapReduce   Map-Reduce is a programming model designed for processing large volumes of data in parallel by dividing the work into a set of independent tasks. Map-Reduce programs are written in a particular style influenced by functional programming constructs, specific idioms for processing lists of data. This module explains the nature of this programming model and how it can be used to write programs that run in the Hadoop environment. MapReduce is a Hadoop framework used for writing applications that can process vast amounts of data on large clusters. It can also be called a programming model in which we can process large datasets across computer clusters. This application allows data to be stored in a distributed form. It simplifies enormous volumes of data and large-scale computing. There are two primary tasks in MapReduce: map and reduce. We perform the former task before the latter. In the map job, we split the input dataset into chunks. Map task processes these c...

 Indexing   Indexing is used to optimize the performance of a database by minimizing the number of disk accesses required when a query is processed. The index is a type of structure having only two columns. The first column comprises a copy of the primary or candidate Key of a table. The Second Column contains a set of pointers for holding the address of the disk block where Specific key values are stored. Advantages of indexing  Better performance of queries. Fast Searching from the database. Fast retrieval of data  Increase performance in SELECT query. Disadvantages of indexing Indexing takes more space. Decrease performance in INSERT, DELETE, and UPDATE query. Figure: Structure of index

We need a temporal database because of the following reasons:- (i) A temporal database efficiently stores a time series of data, typically by having some fixed timescale and then storing only changes in the measured data. (ii) It prevents fragmentation of an object description. (iii) It provides query algebra to deal with temporal data. (iv) It is Compatible with the old databases without temporal data. (v) It maintains the past or historical values and the time at which data was updated.  The different time dimensions in this database that occur on the temporal database are: Valid time, Transaction time, bitemporal data Valid time Valid time is a time period during which a fact is true in the real world. Given a particular event or fact that is associated with a particular time point or time period in the database, the association may be interpreted to mean different things. The most natural interpretation is that the associated time is the time that the event occurred or the peri...

  Multimedia Database  A Multimedia database is the collection of interrelated multimedia data that includes text, graphics (sketches, drawings), images, animations, video, audio, etc., and has vast amounts of multisource multimedia data. The framework that manages different types of multimedia data which can be stored, delivered, and utilized in different ways is known as a multimedia database management system. Multimedia databases provide features that allow users to store and query different types of multimedia information, which includes images (such as photos or drawings), video clips (such as movies, newsreels, or home videos), audio clips (such as songs, phone messages, or speeches), and documents (such as books or articles). The main types of database queries that are needed involve locating multimedia sources that contain certain objects of interest. For example, one may want to locate all video clips in a video database that includes a certain person, say Michael Ja...

  Document Databases Document databases, like JSON (JavaScript Object Notation) objects, store data in documents. Each document has a set of field and value pairs. The values might be of many sorts, such as texts, integers, Booleans, arrays, or objects, and their structures are usually aligned with the objects that developers interact with within code. Document databases are useful for a broad number of use cases and may be utilized as a general-purpose database due to their variety of field value types and strong query languages. They can expand out horizontally to accommodate enormous data volumes. A document database is a type of NoSQL database that stores data as JSON documents instead of columns and rows. JSON is a native language used to both store and query data. These documents can be grouped together into collections to form database systems. Each document consists of a number of key-value pairs.  Here is an example of a document that consists of 4 key-value pairs: { ...

The different techniques for distributed database design are:- 1. Data Fragmentation, 2. Data Replication 3. Data Allocation                                                         1. Data Fragmentation, Fragmentation is the task of dividing a table into a set of smaller tables. The subsets of the table are called fragments. These fragments may be stored at different locations. Moreover, fragmentation increases parallelism and provides better disaster recovery. Fragmentation can be of three types: Vertical Fragmentation Horizontal Fragmentation Hybrid Fragmentation fragmentation should be done in a way so that the original table can be reconstructed from the fragments. This is needed so that the original table can be reconstructed from the fragments whenever required. This requirement is called "reconstructiveness". 2. Data Replication Data Replicat...

Query tree A query tree represents a tree data structure representing relational algebra expression. The tables of query trees are represented as leaf the query nodes The relational algebra operations are represented as the Internal nodes. The root represents the query as a whole. Query Processing is the activities involved in parsing, validating, optimizing, and executing a query. We need this tree in query processing because: It reduces the size of the intermediate relations, both in terms of bytes per record as well as a number of records, as soon as possible so that subsequent operations will have fewer data to process and thus execute quicker. Operations, such as conjunctive selections, Should be broken down into their equivalent Set of Smaller units to allow the individual units to be moved into"better" positions within the query tree. Combining Cartesian products with corresponding selects to create joins-utilizing optimized join algorithms like the sort-merge join and...

Object query language (OQL)  OQL is an SQL-like declarative language that provides a rich environment for efficient querying of database objects, including high-level primitives for object sets and structures.OQL also includes object extensions for object identity, complex objects, path expressions, operation invocation, and inheritance. OQL's queries can invoke operations in ODMG language bindings, and OQL may be embedded in an ODMG language binding. The object query language OQL is the query language proposed for the ODMG object model. It is designed to work closely with the programming languages for which an ODMG binding is defined, such as C++, Smalltalk, and Java. Hence, an OQL query embedded into one of these programming languages can return objects that match the type system of that language. Additionally, the implementations of class operations in an ODMG schema can have their code written in these programming languages. The OQL syntax for queries is similar to the syntax o...

  Specialization Specialization is a process that defines a group of entities that is divided into subgroups based on their characteristic. It is a top-down approach, in which one higher entity can be broken down into two lower-level entities. It maximizes the difference between the members of an entity by identifying the unique characteristic or attributes of each member. It defines one or more subclass for the superclass and also forms the superclass/subclass relationship. For example: Generalization Generalization is the process of generalizing the entities which contain the properties of all the generalized entities. It is a bottom approach, in which two lower-level entities combine to form a higher-level entity. Generalization is the reverse process of Specialization. It defines a general entity type from a set of the specialized entity type. It minimizes the difference between the entities by identifying the common features. For example:

Query optimization Query optimization is the process of selecting an efficient execution plan for evaluating the query. The main goal of query optimization is to choose the best execution strategy for a given query under the given resource constraints. Query optimization reduces the system resources required to fulfill a query, and ultimately provides the user with the correct result. We need query optimization because of the following reasons:-  The goal of query optimization is to reduce the system resources required to fulfill a query and ultimately provide the user with the correct result set faster.  First, it provides the user with faster results, which makes the application seem faster to the user.  Secondly, it allows the system to service more queries in the same amount of time because each request takes less time than unoptimized queries.  Thirdly, query optimization ultimately reduces the amount of wear on the hardware (e.g. disk drives), and allows t...