System development software. Computer languages. Language translation methods.
Language Translation Method - A language translator translates software from the language used by software developers into a computer’s language (known as machine language) and so lets developers use a common language for software designed for many different types of computers. Each computer translates the same software into instructions that it alone can use. Two types of language translators exist: compilers and interpreters A compiler, such as one used for C, COBOL, FORTRAN,PASCAL, translates a program, called source code, written in the developer’s language into computer code called an object module. A linker combines object modules that perform related tasks with already-compiled object code from a library of commonly used functions to create a program called an executable module, or a load module A user can load the executable into a computer and run it. The computer running the executable does not need a copy of the compiler because the program has already been translated. Many languages allow a program to link or unlink an object module as the program runs, a feature called dynamic linking. An interpreter, such as one used for BASIC, translates language commands into computer code one instruction at a time and then executes each instruction before translating the next instruction. The user simply loads the interpreter into the computer and runs it. The interpreter treats the source code as data, reading, translating and obeying its commands. Interpreters have two major advantages relative to compilers: First, the developer can distribute his source code to anyone who has an interpreter. The same source code will run on any computer and in any operating system. This makes interpreted languages, such as JavaScript and HTML, ideal for programming Web pages. In contrast, a developer using a compiled language must create executable modules for each combination of computer type and operating system. Second, an interpreter offers a friendly environment for the software developer. The developer can interrogate the interpreter about the state of the program, reset data values, and continue or restart the program In contrast, every time a developer makes a change in a compiled-language program, it must be recompiled and re-linked before testing and using. Interpretive languages also have several disadvantages. - An interpreted program runs slower than a similar compiled program because it must be translated while it runs. A user running an interpreter program must have a copy of the interpreter on her computer while a user running a compiled program does not need a copy of a compiler. Users of interpreted programs must have access to the source code to run the programs; thus, protecting interpreted software from piracy is much harder than protecting compiled software. Some languages such as BASIC and LISP exist in both interpretive and compiled forms. Developers can develop their software using the interpretive form of the language and distribute their software in the compiled form, but the compiled programs can’t run on any computer. Other languages, such as Java, compile source code into an intermediate code that preserves much of the source code into an intermediate code that preserves much of the source language in a highly compact, incomprehensible form, yet still requires an interpreter. This solution allows the program to remain proprietary, yet run on any computer. It also speeds program execution, although not to the extent of a compiled language. 58. Language translation methods, their pluses and minuses. 59. Data type concept. 60. The concept of structured programming. 61. Two main principles of John von Neumann Computer architecture. 62. Databases. DBMS. Categorization of DBMS. To use the data effectively, the information must be stored in such a way that it can be retrieved and interpreted with flexibility and efficiency. Usually it is done by using databases. A database is an organized collection of related information used for a specific purpose, such as keeping track of ongoing work order activities or maintaining a library. Data Base Management System DBMS is a set of computer programs that controls the – creation, – maintenance, and - use of a database Database management systems:
Ex: MySQL, PostgreSQL, Microsoft Access, SQL Server, FileMaker, Oracle, RDBMS, dBASE, Clipper, FoxPro,etc. Almost every database software comes with an Open Database Connectivity (ODBC) driver that allows the database to integrate with other databases. 63. Database models. Their pluses and minuses Well, essentially a data model is a "description" of both a container for data and a methodology for storing and retrieving data from that container. Actually, there isn't really a data model "thing". Data models are abstractions, oftentimes mathematical algorithms and concepts. You cannot really touch a data model. But nevertheless, they are very useful. The analysis and design of data models has been the cornerstone of the evolution of databases. As models have advanced so has database efficiency. Perhaps the most intuitive way to visualize this type of relationship is by visualizing an upside down tree of data. In this tree, a single table acts as the "root" of the database from which other tables "branch" out. • Relationships in such a system are thought of in terms of children and parents such that a child may only have one parent but a parent can have multiple children. Parents and children are tied together by links called "pointers" • The hierarchical structure is used primarily today for storing geographic information and file systems. the Network model solves the problem of data redundancy by representing relationships in terms of sets rather than hierarchy. The model had its origins in the Conference on Data Systems Languages (CODASYL) which had created the Data Base Task Group to explore and design a method to replace the hierarchical model. • The network model is very similar to the hierarchical model actually. In fact, the hierarchical model is a subset of the network model. However, instead of using a single-parent tree hierarchy, the network model uses set theory to provide a tree-like hierarchy with the exception that child tables were allowed to have more than one parent. This allowed the network model to support many-to-many relationships.
• The network structure consists of more complex relationships. Unlike the hierarchical structure, it can relate to many records and accesses them by following one of several paths. In other words, this structure allows for many-to-many relationships. • Nevertheless, though it was a dramatic improvement, the network model was far from perfect. Most profoundly, the model was difficult to implement and maintain. Most implementations of the network model were used by computer programmers rather than real users. What was needed was a simple model which could be used by real end users to solve real problems. • Of course in the 80's the "Relational Database Model" became the rage. The Relational Model developed out of the work done by Dr. E. F. Codd at IBM in the late 1960s who was looking for ways to solve the problems with the existing models. • Because he was a mathematician, he naturally built the model on mathematical concepts which he expounded in the famous work called "A Relational Model of Data for Large Shared Databanks". • At the core of the relational model is the concept of a table (also called a relation) in which all data is stored. Each table is made up of records (horizontal rows also known as tuples) and fields (vertical columns also known as attributes). • It is important to note that how or where the tables of data are stored makes no difference. Each table can be identified by a unique name and that name can be used by the database to find the table behind the scenes. As a user, all you need to know is the table name in order to use it. You do not need to worry about the complexities of how the data is stored on the hard drive. • This is quite a bit different from the hierarchical and network models in which the user had to have an understanding of how the data was structured within the database in order to retrieve, insert, update, or delete records from the database. • The relational structure is the most commonly used today. It is used by mainframe, midrange and microcomputer systems. It uses two-dimensional rows and columns to store data. The tables of records can be connected by common key values. • While working for IBM, E.F. Codd designed this structure in 1970. The model is not easy for the end user to run queries with because it may require a complex combination of many tables.
Database management systems can be categorized according to
Also databases can be Classified by function and database model I. Function Analytic(al) Operational …….. II. Database model Flat file Hierarchical Network Relationa l An analytical database is used to store information from different types of databases such as selected operational databases and external databases. Other names given to analytical databases are information databases, management databases or multi-dimensional databases. The data stored in an analytical database is used by the management for analysis purposes, hence the name. The data in an analytical database cannot be changed or manipulated. Operational Database - In its day to day operation, an organisation generates a huge amount of data. Think of things such as inventory management, purchases, transactions and financials. All this data is collected in a database which is often known by several names such as operational/ production database, subject-area database (SADB) or transaction databases. An operational database is usually hugely important to organisations as they include the customer database, personal database and inventory database i.e. the details of how much of a product the company has as well as information on the customers who buy them. The data stored in operational databases can be changed and manipulated depending on what the company requires.
Database Warehouse - Organisations are required to keep all relevant data for several years. In the UK it can be as long as 6 years. This data is also an important source of information for analysing and comparing the current year data with that of the past years which also makes it easier to determine key trends taking place. All this data from previous years are stored in a database warehouse. Since the data stored has gone through all kinds of screening, editing and integration it does not need any further editing or alteration. With this database ensure that the software requirements specification (SRS) is formally approved as part of the project quality plan Distributed Databases - Many organisations have several office locations, manufacturing plants, regional offices, branch offices and a head office at different geographic locations. Each of these work groups may have their own database which together will form the main database of the company. This is known as a distributed database. End-User Databases - There is a variety of data available at the workstation of all the end users of any organisation. Each workstation is like a small database in itself which includes data in spreadsheets, presentations, word files, note pads and downloaded files. All such small databases form a different type of database called the end-user database. External Database - There is a sea of information available outside world which is required by an organisation. They are privately-owned data for which one can have conditional and limited access for a fortune. This data is meant for commercial usage. All such databases outside the organisation which are of use and limited access are together called external database. Hypermedia Database - Most websites have various interconnected multimedia pages which might include text, video clips, audio clips, photographs and graphics. These all need to be stored and “called” from somewhere when the webpage if created. All of them together form the hypermedia database. Navigational database has all the items which are references from other objects. In this, one has to navigate from one reference to other or one object to other. It might be using modern systems like XPath. One of its applications is the air flight management systems. A document oriented database is a different type of database which is used in applications which are document oriented. The data is stored in the form of text records instead of being stored in a data table as usually happens. A real-time database handles data which constantly keep on changing. An example of this is a stock market database where the value of shares change every minute and need to be updated in the real-time database. This type of database is also used in medical and scientific analysis, banking, accounting, process control, reservation systems etc. Essentially anything which requires access to fast moving and constantly changing information. Assume that this will require much more time than a normal relational database when it comes to the software testing life cycle, as these are much more complicated to efficiently test within normal timeframes.
64. MS Office Access 2010. Objects, their functions. Creating a table in Access. MS Access is a relational database.As it is mentioned above, in a relational database the information is divided into separate stacks of logically related data, each of which is stored in a separate table in the file. Tables are the fundamental objects at the heart of a relational database. They form the active basis for the information storage and retrieval system. Once the information is arranged in separate tables, you can view, add, edit and delete information with online forms, search for and retrieve some of or all the information with queries; and print information as customized reports. In Access the term database is more precisely used to define the collection of objects that store, track, manipulate, and retrieve data. • Advantages of relational structure - Reduction of data redundancy, which not only reduces the required disk storage space, but also speeds processing. • Flexibility. If data changes, you can update the value in only one place. All queries, forms, and reports look in that place for the current values. • Simplicity. The flat-file model used as the basis for a relational system dictates a simple, non-redundant method of data storage. Each table in the relational design is a single object containing data relevant to a particular aspect of the database, such as an employee, a product, or an order. • Power. Storing the data in separate related tables allows grouping, searching, and retrieving the information in almost unlimited ways. • Ease of management. With smaller, less-complicated tables, the information is much easier to locate and manage. Differences between Access и Excel 3. Excel is convenient to work with if a table contains a limited number of rows. Database tables may contain a huge number of records. Database management system offers effective tools to retrieve necessary information. 7. Excel allows for several users to work with one and the same spreadsheet, but this possibility is limited. Types f relations: Tables can be related in three different ways: – one-to-one, – one-to-many, and – many-to-many. The type you define depends on how many records in each table are likely to have the same value. To relate tables, one of them must include a field that contains a unique value in every record. This can be a primary key field or a field with a unique index that allows no duplicate values. A primary key or a unique index can also be a combination of two or more fields whose combined value is unique for all records. For example, the Employee ID can be a unique number that identifies an employee. If you want to use names in a key or index, you’d probably need to include both the first and last names to ensure unique values. In Access the most commonly used type of relationship is the one-to-many relationship, in which one record in one table can have one or many matching records in another table, or maybe none at all. The table on “one” side is often called the parent table and the other is called the child table. The one-to-one relationship is sometimes used as a form of lookup, in which each record in one of the tables has a matching record in the other table. Neither table is designated as the parent. The key fields in both tables are the primary keys. One use of this type of relationship is to store additional, seldom-accessed information about an item in the first table, such as an abstract of a book or the details of a work order. [ The many-to-many relationship is not permitted as such in a relational database. Many records in one table have the same values in the key field as many records in the second table. To implement this in Access, you must create a third table, called a junction table, to place between the first two, converting the many-to-many to two one-to-many relationships. Office Access 2007 introduces a new field type, the multivalued field, that can replace the need for the junction table when creating a many-to-many relationship.] Referential integrity is an optional system of rules that guarantees the relationships are valid and the database will remain intact as data is entered, edited, or deleted. • The basic rule of referential integrity is this: For every record in a child table (the “many” side), one and only one matching record must be in the parent table (the “one” side). • Some of the Access Rules: You cannot enter a child record for which no parent exists (start a work order without a customer). • You cannot delete a parent record if related child records still exist (remove a customer before the job is completed). • You cannot change a child record so its foreign key does not have a match in the parent table (change the customer field in a work order record to a nonexistent customer). • You cannot change the primary key value in a parent table as long as related records are in the child table (change a customer link before the work order is finished). ] [ Before you can set referential integrity, you must make sure you meet the following conditions: • The matching field in the parent table is the primary key or at least has a unique value, such as AutoNumber field. • Related fields are the same data type. • Both tables are in the same Access database. You can set referential integrity between linked tables, provided they are both in Access format and you open the database that contains the linked tables. • The same rules can apply to a one-to-one relationship. Enforcing the referential integrity rules in such a relationship guarantees that every record in the table has one and only one matching record in the other table. ] Access objects: Access is an object-oriented database management system (DBMS), • The tables are the containers for all the data in your database. A table (entity) represents all that the database knows about one subject or kind of thing. A column (attribute) represents one feature, characteristic, or fact that is true of the table subject. A row (instance) represents one individual instance of the table subject. • A query is a question that you ask of your database. You usually use a query to extract a specified set of records from one or more tables. • Forms are often more convenient than a tabular datasheet for entering and editing table data, especially if a table includes more data than can fit across the screen and you have to scroll right to see the rest. Forms are especially useful for creating a comfortable visual environment for data management. • When you want to print the data, you usually create a report. The report can be a quick and easy dump of the table data — useful for checking specific data items — or it can be a glossy presentation of the data in a custom format suitable for the stockholders or a business manager. • Macros contain a sequence of commands that perform a certain task and are useful for defining the automatic actions that respond to button clicks or other events. • Modules are programs written in Visual Basic for Applications (VBA), the programming language used by Office Access 2007. Procedures contained in the modules are the cornerstone (краеугольный камень) of advanced Access applications. Objects have certain characteristics or attributes called properties that determine their structure, appearance, and behavior. For example, table properties include: - a description of the table, - the subject of the table, and - the arrangement of records in the table, such as in alphabetic or chronological order, based on one or more fields.
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network database model
