Tag Archives: database

Harbour Database Functions

Posted on by vivaclipper

Database Functions

AFields Fills referenced arrays with database field information
Alias Returns the alias name of a work area
BOF Test for the beggining-of-file condition
dbAppend Appends a new record to a database file
dbClearFilter Clears the current filter condiction in a work area
dbCloseAll Close all open files in all work areas.
dbCloseArea Close a database file in a work area
dbCommit Updates all index and database buffers for a given workarea
dbCommitAll Flushes the memory buffer and performs a hard-disk write
dbCreate Creates an empty database from a array
dbDelete Mark a record for deletion in a database
dbEval Performs a code block operation on the current Database
DBF Alias name of a work area
dbFilter Return the filter expression in a work area
dbGoBottom Moves the record pointer to the bottom of the database
dbGoto Position the record pointer to a specific location
dbGoTop Moves the record pointer to the top of the database
dbRecall Recalls a record previousy marked for deletion
dbSeek Searches for a value based on an active index
dbSelectArea Change to another work area
dbSetDriver Establishes the RDD name for the selected work area
dbSetFilter Establishes a filter condition for a work area
dbSkip Moves the record pointer in the selected work area
dbSkipper Helper function to skip a database
dbStruct Builds a multidimensional array of a database structure
dbUseArea Opens a work area and uses a database file
Deleted Tests the record’s deletion flag
EOF Test for end-of-file condition
FCount Counts the number of fields in an active database
FieldDeci Determines the number of decimal places of a given numeric field
FieldGet Obtains the value of a specified field
FieldName Return the name of a field at a numeric field location
FieldPos Return the ordinal position of a field
FieldPut Set the value of a field variable
FieldSize Determines the size of a given field
FieldType Determines the type of a given field
Found Determine the success of a previous search operation
Header Return the length of a database file header
LastRec Returns the number of records in an active work area or database
LUpdate Yields the date the database was last updated
RecCount Counts the number of records in a database
RecNo Returns the current record number or identity
RecSize Returns the size of a single record in an active database
Select Returns the work area number for a specified alias
Used Checks whether a database is in use in a work area

Commands

Posted on by vivaclipper

User Interface

? | ?? Display one or more values to the console
@…BOX Draw a box on the screen
@…CLEAR Clear a rectangular region of the screen
@…GET Build a new Get object and display it to the screen
@…PROMPT Paint a menu item and define a message
@…SAY Display data at a specified screen or printer row and column
@…TO Draw a single- or double-line box
ACCEPT* Place keyboard input into a memory variable
CLEAR TYPEAHEAD Empty the keyboard buffer
DISPLAY Display records to the console
INPUT* Enter the result of an expression into a variable
KEYBOARD Stuff a string into the keyboard buffer
LIST List records to the console
MENU TO Execute a lightbar menu for defined PROMPTs
READ Activate full-screen editing mode using Get objects
RESTORE SCREEN* Display a saved screen
SAVE SCREEN* Save the current screen to a buffer or variable
SET BELL Toggle sounding of the bell during full-screen operations
SET COLOR* Define screen colors
SET CONFIRM Toggle required exit key to terminate GETs
SET CONSOLE Toggle console display to the screen
SET CURSOR Toggle the screen cursor on or off
SET DECIMALS Set the number of decimal places to be displayed
SET DELIMITERS Toggle or define GET delimiters
SET ESCAPE Toggle Esc as a READ exit key
SET FIXED Toggle fixing of the number of decimal digits displayed
SET FORMAT* Activate a format when READ is executed
SET FUNCTION Assign a character string to a function key
SET INTENSITY Toggle enhanced display of GETs and PROMPTs
SET MESSAGE Set the @…PROMPT message line row
SET SCOREBOARD Toggle the message display from READ or MEMOEDIT()
SET TYPEAHEAD Set the size of the keyboard buffer
SET WRAP* Toggle wrapping of the highlight in menus
TEXT* Display a literal block of text
WAIT* Suspend program processing until a key is pressed

Database

APPEND BLANK Add a new record to the current database file
APPEND FROM Import records from a database (.dbf) file or ASCII text file
AVERAGE Average numeric expressions in the current work area
CONTINUE Resume a pending LOCATE
COPY STRUCTURE Copy the current .dbf structure to a new database (.dbf) file
COPY STRUCTURE EXTENDED Copy field definitions to a .dbf file
COPY TO Export records to a database (.dbf) file or ASCII text file
COUNT Tally records to a variable
CREATE Create an empty structure extended (.dbf) file
CREATE FROM Create a new .dbf file from a structure extended file
DELETE Mark records for deletion
DELETE TAG Delete a tag
FIND* Search an index for a specified key value
GO Move the pointer to the specified identity
INDEX Build an index file
JOIN Build new database file by merging from two work areas
LOCATE Search sequentially for a record matching a condition
PACK Remove deleted records from a database file
RECALL Restore records marked for deletion
REINDEX Rebuild open indexes in the current work area
REPLACE Assign new values to field variables
SEEK Search an order for a specified key value
SELECT Change the current work area
SET AUTOPEN Toggles automatic opening of a structural index file
SET AUTORDER Defines the default controlling index for automatically opened index files
SET AUTOSHARE Defines network detection for shared file access
SET DELETED Toggle filtering of deleted records
SET DESCENDING Change the descending flag of the controlling order
SET EXCLUSIVE* Establish shared or exclusive USE of database files
SET FILTER Hide records not meeting a condition
SET INDEX Open one or more order bags in the current work area
SET MBLOCKSIZE Change the block size for memo files
SET ORDER Select the controlling order
SET RELATION Relate two work areas by a key value or record number
SET SCOPE Change the boundaries for scoping keys in controlling order
SET SCOPEBOTTOM Change bottom boundary for scoping keys in controlling order
SET SCOPETOP Change top boundary for scoping keys in controlling order
SET SOFTSEEK Toggle relative seeking
SET STRICTREAD Toggles read optimization for database access
SET UNIQUE* Toggle inclusion of non-unique keys into an index
SKIP Move the record pointer to a new position
SORT Copy to a database (.dbf) file in sorted order
SUM Sum numeric expressions and assign results to variables
TOTAL Summarize records by key value to a database (.dbf) file
UNLOCK Release file/record locks set by the current user
UPDATE Update current database file from another database file
USE Open an existing database (.dbf) and its associated files
ZAP Remove all records from the current database file

Program Execution

CANCEL Terminate program processing
DO* Executes a function or procedure
QUIT Terminate program processing
RUN Execute a OS command or program
SET KEY Assign a procedure invocation to a key
NOTE* Place a single-line comment in a program file
SET PROCEDURE* Compile procedures and functions into the current object file

Variable Management

CLEAR ALL* Close files and release public and private variables
CLEAR GETS Release Get objects from the current GetList array
CLEAR MEMORY Release all public and private variables
CLEAR SCREEN Clear the screen and return the cursor home
RELEASE Delete public and private memory variables
RESTORE Retrieve memory variables from a memory (.mem) file
SAVE Save variables to a memory (.mem) file
STORE* Assign a value to one or more variables
SET EXACT Toggle exact matches for character strings

Device, Files & Folders

CLOSE Close a specific set of files
COMMIT Perform a solid-disk write for all active work areas
COPY FILE Copy a file to a new file or to a device
DELETE FILE Remove a file from disk
DIR* Display a listing of files from a specified path
ERASE Remove a file from disk
RENAME Change the name of a file
SET ALTERNATE Echo console output to a text file
SET DEFAULT Set the application default drive and directory
SET DEVICE Direct @…SAYs to the screen or printer
SET PATH Specify the CA-Clipper search path for opening files
TYPE Display the contents of a text file

Printer

EJECT Advance the printhead to top of form
SET MARGIN Set the page offset for all printed output
SET PRINTER Toggle echo of output to printer or set the print destination

Label / Report

LABEL FORM Display labels to the console
REPORT FORM Display a report to the console

Date & Time

SET CENTURY Modify the date format to include or omit century digits
SET DATE Set the date format for input and display
SET EPOCH Control the interpretation of dates with no century digits

All

SP_REPORTER

Posted on by vivaclipper 
REPORTER()

  Short:
  ------
  REPORTER() Create, modify, execute reports

  Returns:
  --------
  Nothing

  Syntax:
  -------
  REPORTER([aFieldNames,aFieldTypes,aFieldLengths])

  Description:
  ------------
  Build/modify reports based on fields in database.
  Fields in database may be specified in arrays 1-3 which are
  [aFieldNames] field names [aFieldTypes] field types and
  [aFieldLengths] field lengths. All fields are used by default.

  Reporter allows a MAJOR and MINOR group, using the
  indexes currently available and open.

  Examples:
  ---------
   example 1:

   Use Customer
   REPORTER()

   example 2:
   USE Customer
   aFieldNames := {"fname","lname","mi"}
   aFieldTypes := {"C","C","C"}
   aFieldLens  := {15,35,1}
   REPORTER(aFieldNames,aFieldTypes,aFieldLens)

  Notes:
  -------
  Reporter() reports are stored in a DBF file. See the
  index for file structures. See SLSF_REPORT() for further info on
  the name and location of this file.

  Upgrade note:
  The look and feel have changed to one more uniform
  with other SuperLib functions.

  Source:
  -------
  R_REPORT.PRG

See Also : SLSF_REPORT()

Code blocks, inside and out

Posted on by vivaclipper

 

Code blocks, inside and out

 

A Database Primer

Posted on by vivaclipper

Databases (PDF)

Author : G.C. Reddy

Database Terms

Posted on by vivaclipper

Alias :

The name of a work area; an alternate name given to a database file. Aliases are often used to give database files descriptive names and are assigned when the database file is opened. If no alias is specified when the database file is USEd, the name of the database file becomes the alias.

An alias can be used to reference both fields and expressions (including user-defined functions). In order to alias an expression, the expression must be enclosed in parentheses.

See also : Work Area

Attribute :

As a formal DBMS term, refers to a column or field in a table or database file.

See Also: Column, Field

Beginning of File :

The top of the database file. In Clipper language there is no beginning of file area or record. Instead, it is indicated by BOF() returning true (.T.) if an attempt is made to move the record pointer above the first record in the database file or the database file is empty.

Cell :

In a table, a cell is the intersection of a Row and a Column.

Column :

A database term used to describe a field in a table or database file.

See Also: Field

Concurrency :

The degree to which data can be accessed by more than one user at the same time.

Condition :

A logical expression that determines whether an operation will take place. With database commands, a logical expression that determines what records are included in an operation. Conditions are specified as arguments of the FOR or WHILE clause.

See Also: Scope

Controlling/Master Index :

The index currently being used to refer to records by key value or sequential record movement commands.

See Also: Index, Natural Order

Database :

An aggregation of related operational data used by an application system. A database can contain one or more data files or tables.

See Also: Field, Record, Tuple, View

DBMS :

An acronym for the term database management system. A DBMS is a software system that mediates access to a database through a data manipulation language.

Delimited File :

A text file that contains variable-length database records with each record separated by a carriage return/linefeed pair (CHR(13) + CHR(10)) and terminated with an end of file mark (CHR(26)). Each field within a delimited file is variable length, not padded with either leading or trailing spaces, and separated by a comma. Character strings are optionally delimited to allow for embedded commas.

End of File :

The bottom of a database file. In Clipper language, this is LASTREC() + 1 and is indicated by EOF() returning true (.T.).

Field :

The basic column unit of a database file. A field has four attributes: name, type, length, and decimals if the type is numeric.

See Also: Database, Record, Tuple, Vector, View

Field Variable :

A variable that refers to data in a database field, as opposed to data in memory.

See Also: Local Variable, Memory Variable, Variable

Index :

An ordered set of key values that provides a logical ordering of the records in an associated database file. Each key in an index is associated with a particular record in the database file. The records can be processed sequentially in key order, and any record can be located by performing a SEEK operation with the associated key value.

See Also: Controlling/Master Index, Key Value, Natural Order

Join :

An operation that takes two tables as operands and produces one table as a result. It is, in fact, a combination of other operations including selection and projection.

See Also: Projection, Selection

Key Expression :

An expression, typically based on one or more database fields, that when evaluated, yields a key value for a database record. Key expressions are most often used to create indexes or for summarization operations.

See Also: Index, Key Value

Key Value :

The value produced by evaluating a key expression. When placed in an index, a key value identifies the logical position of the associated record in its database file.

See Also: Index, Key Expression

Master Index :

The index currently being used to refer to records by key value or sequential record movement commands.

See Also : Controlling/Master Index

Memo Type :

A special database field type consisting of one or more characters in the extended character set. The maximum size of a memo field In Clipper language is 65,534 bytes. A memo field differs only from a character string by the fact it is stored in a separate memo (.DBT file) and the field length is variable-length.

See Also: Character String

Natural Order :

For a database file, the order determined by the sequence in which records were originally entered into the file. Also called unindexed order.

See Also: Index

Normalization :

The process of elimination and consolidation of redundant data elements in a database system.

Projection :

A DBMS term specifying a subset of fields. In Clipper, the analogy is the FIELDS clause.

See Also: Join Selection

Query :

A request for information to be retrieved from a database. Alternately, a data structure in which such a request is encoded.

Record :

The basic row unit of a database file consisting of one or more field elements.

See Also: Database, Field, Table, Tuple

Relation :

A link between database files that allows the record pointer to move in more than one database file based on the value of a common field or expression. This allows information to be accessed from more than one database file at a time.

Relational Database System :

A system that stores data in rows and columns, without system dependencies within the data. In other words, relationships between different databases are not stored in the actual database itself, as is the case in a system that uses record pointers.

Row :

A group of related column or field values that are treated as a single entity. It is the same as a Clipper language record.

See Also: Column, Field, Record

Search Condition :

See : Condition, Scope

Scope :

In a database command, a clause that specifies a range of database records to be addressed by the command. The scope clause uses the qualifiers ALL, NEXT, RECORD, and REST to define the record scope.

See Also: Condition

SDF File :

A text file that contains fixed-length database records with each record separated by a carriage return/linefeed pair (CHR(13) + CHR(10)) and terminated with an end of file mark (CHR(26)). Each field within an SDF file is fixed-length with character strings padded with trailing spaces and numeric values padded with leading spaces. There are no field separators.

See Also: Database, Delimited File, Text File

Selection :

A DBMS term that specifies a subset of records meeting a condition. The selection itself is obtained with a selection operator. In Clipper language, the analogy is the FOR clause.

Separator :

The character or set of characters that differentiate fields or records from one another. In Clipper language, the DELIMITED and SDF file types have separators. The DELIMITED file uses a comma as the field separator and a carriage return/linefeed pair as the record separator. The SDF file type has no field separator, but also uses a carriage return/linefeed pair as the record separator.

See Also: Delimiter

Sort Order :

Describes the various ways database files and arrays are ordered.

. Ascending

Causes the order of data in a sort to be from lowest value to highest value.

. Descending

Causes the order of data in a sort to be from highest value to lowest value.

. Chronological

Causes data in a sort to be ordered based on a date value, from earliest to most recent.

. ASCII

Causes data in a sort to be ordered according to the ASCII Code values of the data to be sorted.

. Dictionary

The data in a sort is ordered in the way it would appear if the items sorted were entries in a dictionary of the English language.

. Collating Sequence

Data in a sort will be placed in sequence following the order of characters in the Extended Character Set.

. Natural

The order in which data was entered into the database.

Table :

A DBMS term defining a collection of column definitions and row values. In Clipper, it is represented and referred to as a database file.

Tuple :

A formal DBMS term that refers to a row in a table or a record in a database file. In DIF files, tuple also refers to the equivalent of a table record.

See Also: Database, Field, Record

Update :

The process of changing the value of fields in one or more records. Database fields are updated by various commands and the assignment operator.

Vector :

In a DIF file, vector refers to the equivalent of a table field.

See Also: Database, Field, Record, Tuple

View :

A DBMS term that defines a virtual table. A virtual table does not actually exist but is derived from existing tables and maintained as a definition. The definition in turn is maintained in a separate file or as an entry in a system dictionary file. In Clipper, views are supported only by DBU.EXE and are maintained in (.vew) files.

See Also: Database, Field, Record

Work Area :

The basic containment area of a database file and its associated indexes. Work areas can be referred to by alias name, number, or a letter designator.

See Also: Alias

Clipper Description

Posted on by vivaclipper

Developed by Nantucket software and released in winter of 1984, first shipping 25 May 1985.

Clipper was a typical database development language and DOS based. Originally is was used as a replacement programming language for Ashton Tate’s dbase II database environment that could be compiled and executed as a standalone application.

Millions of applications were built typically for businesses dealing with small databases like client management, stock keeping. Many applications for banking and insurance companies were developed were the application was considered too small to be developed and run on mainframes. Clipper often served as a front end exactly for the above mentioned mainframe applications and did very well in this area.

One of the language’s features: the possibility to link ‘C’ and machine language objects made it a virtual unlimited expandable environment. When you missed a feature, an interface or whatever you could program that yourself and the extension made a reusable part of your toolbox. Libraries were also made by third parties but the programmer could also create its own library or enhance the existing ones.

One of the disadvantages, for commercial developers at least, was that a clipper executable could easily be disassembled or de-compiled to produce native source code. There were even commercial packages for that. Between the manufacturers of decompilers and Clipper a covenant was agreed that with a certain code in the source the decompilers would not decompile. But for the hard core hackers no door was kept close.

Around the early 1990’s the users felt a need for a more object oriented environment. Nantucket’s answer was: Clipper 5.0 up to 5.3. This made the Clipper language more sophisticated, but completely OO it never was. Objects and classes could be created but the language needed more, and quickly, should it keep its programmers corps it had created since 1984.

Too late the Nantucket company realized it had to port the Clipper environment to the Windows platform as well and began developing a new project: Aspen: Clipper for Windows. Too late, or at least the research was not given top priority for research and development. In August 1994 (Shipped December 1995) a first version became available and was called: Clipper VO (virtual objects) It was truly windows based but had to cope with many typical first issue bugs that were not explained to the full extend. Again programmers had to build new work arounds and did not feel very comfortable with that idea.

The old stock of programmers however had already switched to Visual Basic (Microsoft) and later Delphi (Borland) This came about because many customers with small database environments wanted to upgrade to window versions in their turn pressured by their clients. And as usual clients wanted their applications yesterday!

A second reason why Clipper never got its previous user base back was that the transition to Clipper VO proved to be too complicated for many senior programmers, and juniors already learned to program in Delphi or VB and later Java.

That was a pity because VO proved to be a very powerful and sophisticated database development tool.

Though Nantucket / CA promised a high degree of compatibility with older developments this did not materialize to the degree to make life easier to former Clipper programmers. The result was that programs were rebuilt in the new environments, the best way to do porting actually. Again slimming down the market for Clipper programmers.

In 1995 Computer Associates bought up the Clipper environment, killed the Clipper DOS version and pre-matured project Aspen, and further developed VO

Other developments for Clipper:

Clipper also could be converted to run on UNIX systems by using a porting tool called Flagship. It runs suitably well.

XBase++ is an OO environment and translates DOS Clipper to Windows but does not enhance the clipper development to an event driven application.

Clip-4-Win is a 16 bit compiler and generated character based applications that ran fairly well within Windows.

Harbour  Clipper got a new life with the Harbour project.

The Harbour-project was started as an open source project in early 1999, the project is still on.

The Harbour programming language is a superset of the well known x-Base language, often referred to as Clipper. Harbour is 100% backward compatible with the Clipper Language, yet it adds many modern features and tools comparable to today’s leading compilers.

Out of the harbour-project, xHarbour (extended Harbour) was started late 2001 as a fork off of the Harbour Project

Clipper is still alive!

Chronology:

1984 first issue: Winter 1984

1990 first issue: Clipper 5.0 (distributed at DefCon fall 1990)

1994 first issue of Clipper VO

1997 Clipper VO 2.5

1999 An open source project: Harbour takes up the challenge

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note : This post gathered from here.