Parcial 2 Flashcards by Jalkem Morales

Q

This is a markup language that was defined by the World Wide Web Consortium (W3C) for general use on the Web.

A

XML

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Q

They define the name of values associate to tags in XML schemes.

A

XML-Attributtes

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Q

All of the information in XML elements must be expressed as character data. But the question is: how do we represent encrypted elements or secure hashes?

A

Binary data

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Q

This is used to enable clients to communicate with web services and for defining the interfaces and other properties of web services.

A

XML-Service

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Q

Every start tag has a matching end tag and all tags are correctly nested, these are:

A

Basic rule

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Q

They are tagged with ‘markup’ strings. The tags are used to describe the logical structure of the data and to associate attribute-value pairs with logical structures.

A

XML data items

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Q

XML is ______ in the sense that users can define their own tags, in contrast to HTML, which uses a fixed set of tags

A

Extensible

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Q

The structure of an XML document is defined by pairs of these elements enclosed in angle brackets.

A

Tags

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Q

The first one was designed for defining the appearance of web pages while the second one was designed for writing structured documents for the Web

A

HTML and XML

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Q

This defines the elements and attributes that can appear in a document, how the elements are nested and the order and number of elements, and whether an element is empty or can include text.

A

An XML schema

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Q

This is a set of names for a collection of element types and attributes that is referenced by a URL.

A

An XML namespace

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Q

They are a simple list of types and content - structs and arrays are the most complex types available.

A

XML-RPC parameters

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Q

This uses the HTTP protocol to pass information from a client computer to a server computer and uses a small XML vocabulary to describe the nature of requests and responses.

A

XML-RPC

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Q

This protocol is based on a trio of communication primitives: doOperation, getRequest and sendReplay.

A

the request-replay protocol

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Q

This scheme involves the management of messages and requires that each message have a unique element by which it may be referenced

A

Message identifiers

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Q

Every XML document must have this as its first line and must at least specify the version of XML in use (which is currently 1.0).

A

A prolog

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Q

This specifies a procedure name and parameters in the XML request, and the server returns either a fault or a response in the XML response.

A

XML-RPC client

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Q

As its name indicates, it is a mechanism to call a procedure or a function available on a remote computer.

A

RPC

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Q

In this form of communication, the sending and receiving processes synchronize at every message. In this case, both send and receive are blocking operations.

A

The synchronous communication

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Q

In this form of communication, the use of the send operation is non-blocking, the receive operation can have blocking and non-blocking variants.

A

The asynchronous communication

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Q

We can describe this as the guarantee to deliver the message despite a reasonable number of packets being dropped or lost

A

Reliability

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Q

This consist of transmitting a message between a socket in one process and a socket in another process.

A

Inter-process communication

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Q

Any process may make use of multiple of these elements to receive messages, but a process cannot share them with other processes on the same computer

A

Ports

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Q

The Internet protocols, and the local port pairs define the:

A

The message destination

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Both forms of communication (UDP and TCP) use ________, which provides an endpoint for communication between processes

The socket abstraction

This is sent by UDP is transmitted from a sending process to a receive process without acknowledgement or retries.

A datagram

Message passing between a pair of processes can be supported by two message communication operations:

Send and receive operations

Messages may be dropped occasionally, either because of a checksum error or because no buffer space is available at the source or destination, it’s called:

Omission failures

This assume that when a pair of processes are establishing a connection, one of them plays the client role and another plays the server role, but thereafter they could be peers.

The API for stream communication

The TCP protocol uses an acknowledgement scheme. If the sender does not receive an acknowledgement with a time out, it retransmits the message and this is performed when:

There is lost messages

This defines reliable communication for channels in terms of two properties: integrity and validity

A failure model

They are three alternative approaches to external data representation.

XML, CORBA and Java´s object serialization.

This was originated from BSD 4.x UNIX and provides the abstraction of a stream of bytes to which data may be written and from which data may be read

The API to the TCP protocol

This is the process of taking a collection of data items and assembling or disassembling (respectively) into a form suitable for transmission in a message

Marshalling and Un-marshalling

The TCP protocol attempts to match the speeds of the processes that read from and write to a stream, this is called:

Flow control

These items transmitted in messages can be data values of many different types, and not all computers store primitive values such as integers in the same order.

The individual primitive data

Who are responsible for the organization, storage, retrieval, naming, sharing and protection of files?

File systems

Sequence of data items (typically 8-bit bytes), accessible by operations to read and write any portion of the sequence.

Data

Single record containing information such as the length of the file, timestamps, file type, owner’s identity and access control lists.

Attributes

Are designed to store and manage large numbers of files, with facilities for creating, naming and deleting files.

File systems

Is a file, often of a special type, that provides a mapping from text names to internal file identifiers.

Directory

Used to refer to all of the extra information stored by a file system that is needed for the management of files.

Metadata

Relates file names to file IDs

Directory module

Relates file IDs to particular files

File module

Checks permission for operation requested

Access control module

Reads or writes file data or attributes

File access module

Accesses and allocates disk blocks

Block module

Disk I/O and buffering

Device module

Adds an entry to a directory and increments the reference count field in the file’s attribute record

AddName

Removes an entry from a directory and decrements the reference count. If this causes the reference count to reach zero, the file is removed.

UnName

Is provided to enable clients to examine the contents of directories and to implement pattern-matching operations on file names such as those found in the UNIX shell. Returns all or a subset of the names stored in a given directory.

GetNames

The interface is suitable for implementation by stateless servers. Stateless servers can be restarted after a failure and resume operation without any need for clients or the server to restore any state.

Stateless servers

In the UNIX file system, the user’s access rights are checked against the access mode (read or write) requested in the open call and the file is opened only if the user has the necessary rights.

Access control

Used in the access rights check is retrieved during the user’s earlier authenticated login and cannot be tampered with in non-distributed implementations.

User Identity (UID)

Is made whenever a file name is converted to a UFID, and the results are encoded in the form of a capability, which is returned to the client for submission with subsequent requests.

Access Check

These are the system calls implemented by the kernel. It is given the primitives here as an indication of the operations that file services are expected to support and for comparison with the file service interfaces.

Operation on files

The need for concurrency control for access to shared data in many applications is widely accepted and techniques are known for its implementation. Most current file services follow modern UNIX standards in providing advisory or mandatory fileor record-level locking.

Concurrent File Updates

Tolerance of disconnection or server failures requires file replication, which is more difficult to achieve.

Fault tolerance

This refers to a model for concurrent access to files in which the file contents seen by all of the processes accessing or updating a given file are those that they would see if only a single copy of the file contents existed.

Consistency

The service interfaces should be defined so that client and server software can be implemented for different operating systems and computers.

Openness (Hardware and operating system heterogeneity)

The design of the file service should support many of the transparency requirements for distributed systems

Access, Location, Mobility, Performance and Scaling transparency

In distributed file systems, there is a need to authenticate client requests so that access control at the server is based on correct user identities and to protect the contents of request and reply messages with digital signatures and (optionally) encryption of secret data.

Security

A distributed file service should offer facilities that are of at least the same power and generality as those found in conventional file systems and should achieve a comparable level of performance.

Efficiency

(FSA) Provides a mapping between text names for files and their UFIDs. The directory service provides the functions needed to generate directories, to add new file names to directories and to obtain UFIDs from directories.

Directory Service

(FSA) Runs in each client computer, integrating and extending the operations of the flat file service and the directory service under a single application programming interface that is available to user-level programs in client computers. Holds information about the network locations of the flat file server and directory server processes.

Client Module

(FSA) Each export an interface for use by client programs, and their RPC interfaces, taken together, provide a comprehensive set of operations for access to files.

Flat File Service and the Directory Service

(Flat File Service Interface) Copies the sequence of n data items beginning at item i from the specified file into Data, which is then returned to the client.

Read

(Flat File Service Interface) Copies the sequence of data items in Data into the specified file beginning at item i, replacing the previous contents of the file at the corresponding position and extending the file if necessary.

Write

(Flat File Service Interface) Creates a new, empty file and returns the UFID that is generated.

Create

(Flat File Service Interface) Removes the specified file.

Delete

Enable clients to access the attribute record.The values of the length and timestamp portions of the attribute record are not affected by __________; they are maintained separately by the flat file service itself

GetAttributes and SetAttributes