Application Programming Interface (API) A set of function and call programs that allow clients and servers to inter- communicate Client A networked information requester, usually a PC or workstation, that can query database and/or other information from a server Middleware A set of drivers, API’s, or other software that improves connectivity between a client application and a server Relational Database A database in which information access is limited to the selection of rows that satisfy all search criteria Server A computer, usually a high- powered workstation or a mainframe, that houses information for manipulation by networked clients Structured Query Language (SQL) A language developed by IBM and standardized by ANSI for addressing, creating, updating, or querying relational databases

There is a heavy reliance on bringing user- friendly applications to the user on his or her system Emphasis on centralizing corporate databases and many network management and utility functions Emphasis on open and modular systems Networking is fundamental to the operation

Standardized interfaces and protocols between clients and back-end databases Hides complexity of data sources from the end-user Compatible with a range of client and server options All applications operate over a uniform applications programming interface (API)

Reliability versus Unreliability Reliable facilities guarantee delivery if possible Such a facility would make use of a reliable transport protocol or similar logic to perform error checking, acknowledgment, retransmission, and reordering of misordered messages Blocking versus Nonblocking Non-blocking is more efficient, but difficult to test and debug programs Blocking (synchronous) retains control until acknowledgment is received

Binding specifies how the relationship between a remote procedure and the calling program will be established Formed when two applications have made a logical connection and are prepared to exchange commands and data Nonpersistent binding A logical connection is established between the two processes at the time of the RPC and as soon as the values are returned, the connection is dismantled Inappropriate for remote procedures that are called frequently by the same caller because of the overhead involved in establishing connections Persistent binding A connection that is set up for an RPC is sustained after the procedure return Maintains the logical connection and allows a sequence of calls and returns to use the same connection

Clients and servers ship messages back and forth between objects May rely on an underlying message or RPC structure or be developed directly on top of object-oriented capabilities in the operating system Success depends on standardization of the object mechanism Competing designs: Microsoft’s Component Object Model (COM), the basis for Object Linking and Embedding (OLE) Common Object Request Broker Architecture (CORBA) developed by the Object Management Group Supported by IBM, Apple, Sun

Implementation of Internet technologies within a corporate organization rather than for external connection to the global Internet Concept has resulted in the most rapid change of direction in the history of business data communication Enabling technologies are the high processing speed and storage capacity of personal computers together with the high data rates of LANs Web technology is responsible for the almost instant acceptance of intranets

Rapid prototyping Scales effectively Little training required Can be implemented on a variety of systems Open architecture allows interaction across platforms Supports a range of distributed servers Allows integration of legacy systems on client and server side Supports a range of media types Inexpensive to implement

Advantages Ease of administration Deployment Development speed Flexible information presentation Disadvantages Limited functionality Stateless operation makes tracking difficult

Client/Server disadvantages include: Long development cycles Difficulty of partitioning applications into client and server modules and modifying the partition in response to user feedback Effort involved in distributing upgrades to clients Difficulty of scaling the servers to respond to increased load in a distributed environment Continuous requirement for increasingly powerful desktop machines Intranet Web has the advantages of: Ease of deployment Use of a small number of widely accepted standards Integration with other TCP/IP- based applications

Makes use of TCP/IP and their applications, especially the Web The distinguishing feature is that it provides access to corporate resources by outside clients This outside access can be through the Internet or through other data communications networks Provides more extensive access to corporate resources, usually in a fashion that enforces a security policy Typical model of operation is client/server

Reduced costs Minimizes paperwork and human involvement Coordination Critical information can be made available so that quick decisions can be made Customer satisfaction Provides more information about the current status of products and services Expedited communication Increases the efficiency and effectiveness of communication

Long- distance dial-up access Internet access to intranet with security Internet access to an external server that duplicates some of a company’s intranet data Internet access to an external server that originates database queries to internal servers Virtual private network

Coarse-grainedInterface-based designDiscoverableSingle instanceLoosely coupledAsynchronous

NIST defines cloud computing as: “A model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models.”

Software as a Service (SaaS) The capability provided to the consumer is to use the provider’s applications running on a cloud infrastructure Saves the complexity of software installation, maintenance, upgrades, and patches Platform as a Service (PaaS) The capability provided to the consumer is to deploy onto the cloud infrastructure consumer- created or acquired applications created using programming languages and tools supported by the provider Often provides middleware- style services Infrastructure as a Service (IaaS) The capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications Enables customers to combine basic computing services such as number crunching and data storage to build highly adaptable computer systems

Hybrid Cloud The cloud infrastructure is a composition of two or more clouds that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability Community Cloud The cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns Private Cloud The cloud infrastructure is operated solely for an organization Public Cloud The cloud infrastructure is made available to the general public or a large industry group and is owned by an organization selling cloud services

NIST establishes a reference architecture described as follows: “The NIST cloud computing reference architecture focuses on the requirements of ‘what’ cloud services provide, not a ‘how to’ design solution and implementation. The reference architecture is intended to facilitate the understanding of the operational intricacies in cloud computing. It does not represent the system architecture of a specific cloud computing system, instead it is a tool for describing, discussing, and developing a system-specific architecture using a common framework of reference.”

NIST developed the reference architecture with the following objectives in mind: To illustrate and understand the various cloud services in the context of an overall cloud computing conceptual model To provide a technical reference for consumers to understand, discuss, categorize, and compare cloud services To facilitate the analysis of candidate standards for security, interoperability, and portability and reference implementations

Figure 9.20 NIST Cloud Computing Reference Architecture

The growth of client/server computing Client/server applications Database applications Classes of client/server applications Three-tier client/server architecture Cloud computing Cloud computing elements Cloud computing reference architecture Chapter 9: Client/Server, Intranet, and Cloud Computing Middleware Middleware architecture Message passing Remote procedure calls Object-oriented mechanisms Intranets Web content Web/Database applications Intranet Webs versus traditional client/server Service-oriented architecture Extranets