DATACOM

About This Presentation

Title:

DATACOM

Description:

Databases: A CA-Datacom/DB information base can include up. To 5,000 databases. ... Index Area (IXX): The Index Area provides fast access to the data. Each ... – PowerPoint PPT presentation

Number of Views:876

Avg rating:3.0/5.0

Slides: 50

Provided by: Rol646

Category:

more less

Transcript and Presenter's Notes

Title: DATACOM

1
DATACOM

VIJAYKUMAR.R
2
DATACOM

Databases A CA-Datacom/DB information base can
include up
To 5,000 databases. Each database consists of an
Index Area
and 1 to 240 data areas.
Data Areas
A data area provides the physical storage for
data tables. A database can
have multiple data areas. Each data area can
support 1 to 240 tables, but
a database is limited to 240 tables as well.
Every data area is a data set
or file. You can assign several tables to the
same area or each table to a
separate area.Placing multiple tables in the
same area can increase
Processing speed when Applications normally
access the tables together
with the same key.

3
Datacom Contd.,

Index Area (IXX) The Index Area provides fast
access to the data. Each
database contains one Index Area which provides
accessibility to all data
areas within that database. The index allows any
table in the database to
be retrieved based on the contents of the table.
CA-Datacom/DB places
an entry in the index for each key within each
table in the database.
Tables All data is stored in tables. Tables are
two-dimensional,
logically made up of rows (records) and columns
(fields). Tables
are easily extendable with the addition of both
rows and columns.
Columns Columns are the smallest data
structures in the Information
base. For SQL access, columns are the unit of
transfer between the
database and the application program. Through
Data dictionary, columns
Are defined using the FIELD entity-type.

Elements For access with CA-Datacom/DB
commands, columns make
up elements and elements are the unit of
transfer. You can define 255
elements per table.
Keys Keys are structures used to optimize data
access or order data
Retrieval. A key is composed of columns. The
columns can be in any
sequence. Each key can be up to 180 characters
long.
You can define up to 99 keys per table or 999 per
database. Any key can
be defined as unique, that is, requiring that
each row in the table have a
unique value for the key.
All tables must have a Master Key and a Native
Key defined. The Master
Key functions as any other key but it can be
defined as updateable or non-
updateable. The Native Key dictates the physical
sequence in which the
data is stored. The Native Key can be the same
as the Master Key.

Master Key Every table must have a Master Key.
A table's Master Key
may be The same as its Native Key.
There is method of preventing duplicate values
in Master key. This
method involves the TABLE attribute
DUPE-MASTER-KEY which
specifies whether duplicate values are permitted
in the Master Key.
This option differs from the KEY attribute UNIQUE
in the following ways
DUPE-MASTER-KEY can only be defined through
Datadictionary.
UNIQUE can be defined through Datadictionary or
SQL.
It may only be specified for one key (the Master
Key) per table. UNIQUE
may be specified for any number of keys.
Attempted violations to DUPE-MASTER-KEY receive
CA-Datacom/DB
return code 10. Attempted violations to a
UNIQUE KEY receive CA-
Datacom/DB return code 94 (internal return code
193).

Native Key
Every table must have one, and only one, Native
Key. This
key designates the sequence in which the data is
loaded and
maintained. Often used in sequential processing.
Dataviews
Dataviews are special structures used by CA-Ideal
and CA-Meta
COBOL. Dataviews provide a logical view of the
data. They can
be composed of elements or keys.

Primary Keys
Each table may have one primary key. A primary
key provides a
guaranteed method of addressing each row in a
table. The primary key
value for each row is unique within the table.
Defining a primary key
through SQL results in a key with the UNIQUE
attribute. The resulting key
is also that table's Master and Native Key,
unless the primary key is being
added to an existing table which already has a
(different) Master and
Native Key.
Foreign Keys
Foreign keys define relationships between tables.
The column(s) of a
foreign key in one table are related to the
primary or unique key of some
table. Every foreign key is related to a primary
or unique key. A primary
or unique key can be related to zero, one, or
many foreign keys.

CA-Datacom/DB Modes of Operation
CA-Datacom/DB has two modes of operation
Multi-User and
Single User. The recommended mode is Multi-User.
Multi-User The Multi-User mode enables
CA-Datacom/DB to access a database concurrently
from multiple regions. The Multi-User Facility is
the manager of the system. It receives a request
from the application and determines how it should
be processed. It coordinates the activities that
must take place to service the request.
Single User The Single User mode allows only
one region to access a database.

DBUTLTY CA-Datacom/DB provides a single
utility, the CA-Datacom/DB
Utility (DBUTLTY), that performs all operations
for creating and
maintaining your information base. You invoke
the functions by entering
commands to the utility program.
Eg
//UTLTY30 EXEC PGMDBUTLTY,COND(0,NE)
//
// UTLTY30 - DISABLE DATA BASE 168 -
AGENT
//
//CXX DD DSND1A.MUFI1.CXX,
// DISPSHR
//SYSPRINT DD SYSOUT
//SYSUDUMP DD SYSOUTU,
// HOLDYES
//ABNLTERM DD SYSOUT
//SNAPER DD SYSOUT
//LOCKDD DD DSNK1C.KFS.DB168.DSLOCK,
// DISPOLD

To create a complete backup of a database using
DBUTLTY, execute
the BACKUP DBIDn function with the control
statement coded
SEQPHYSICAL, RECIDYES,UPDATEYES. This safe
backup can
only be done with the area not open for update
by any application.
When you are backing up a table or area, suspend
all update activity to it.

Accessing CA-Datacom/DB Databases from
Applications
Applications can access CA-Datacom/DB databases
by including CA-
datacom/DB commands or SQL statements in their
code.
CA-Datacom/DB commands are included within a call
to a CA-
Datacom/DB entry point. These calls can be
included in applications
written in Assembler, C language, COBOL, FORTRAN,
and PL/I.
CA-Datacom/DB commands provide two access
techniques
record-at-a-time (RAAT) and set-at-a-time (SAAT).
RAAT
The record-at-a-time commands access data rows
(records) and Index
entries.The rows are selected by specifying a
previously defined key name
and a key value.

RAAT
The rows are retrieved in the sequence of the
key, in either ascending or
descending order. A record with the exact,
greater-than-or-equal, or less-than-or-
equal key value specified may be selected.
SAAT
With the set-at-a-time access technique, a set of
records is defined based on the
data values contained in a table. A set can be
just one record, or an entire table.
Once a set has been defined, individual records
within the set can be accessed.
Records contained in a set are selected by
specifying a search condition. A
search condition is a compound Boolean expression
composed of predicates
joined by the logical operators AND and OR.
Relational operators used in the search are
EQ, LT, GT, LE, GE, NE
Eg VENDR-NAME EQ HCLT AND BR-PIN-CODE GE 600034

Accessing CA-Datacom/DB Databases Using Other
Computer Associates Products
CA-Ideal CA-Ideal enables you to develop and
maintain applications that can
access CA-Datacom/DB databases. CA-Ideal passes
CA-Datacom/DB
commands to the CA-Datacom/DB entry point. It
uses both record-at-a-time and
set-at-a-time access techniques. CA-Ideal also
offers you the option of using
SQL statements within your CA-Ideal programs.
CA-Dataquery CA-Dataquery is an information
retrieval and data manipulation
facility. It allows end users to create queries
that retrieve information from a CA-
Datacom/DB database. CA-Dataquery can access
CA-Datacom/DB using CA-
Datacom/DB commands or SQL statements.
CA-Dataquery also provides a
Personal Database Facility which allows users to
create and maintain personal
tables.

Creating Databases
Each CA-Datacom/DB database can contain from 1 to
240 tables.
Information stored in one database is independent
of that in other databases.
Information in the same database is indexed in
the same Index Area
(IXX).Therefore, a disk error on the Index Area
affects all tables in the
database.
It is best to use a separate database for data
that is relatively unrelated.
For example, use separate databases for
Independent application systems, such as accounts
payable, general ledger, or inventory.
Information about independent subjects, such as
customer information, inventory information or
accounting information.

The steps required for creating CA-Datacom/DB
databases are
Design the logical structure for the databases.
Design the physical attributes for the databases.
Use Datadictionary to define the databases,
areas, tables, columns, keys and
elements.
Catalog the definitions to the CA-Datacom/DB
Directory (CXX).
Allocate and initialize the required data areas
and Index Areas.
Use programs or utilities to actually load data
in the tables.

16
Designing Tables

Each table in a database is an unordered
collection of rows records). A row is a
collection of column (field) values.
The minimum size for a row in a CA-Datacom/DB
table is 1 byte and the maximum is 32720 bytes.
Before you define a table to Datadictionary, you
must define a data area, the physical location
for one or more tables.

Designing Columns
A column (FIELD occurrence) is the smallest data
structure in CA-Datacom/DB. You must define at
least
one column to a table.You can define up to 500
columns to a single table.

Data Types DATE, TIME, and TIMESTAMP
DATE, TIME, and TIMESTAMP are special SQL data
types that are stored and manipulated in
CA-Datacom/DB as binary data with lengths 4, 3,
and 10 respectively.
In COBOL, the data type of the host variable to
receive or send a DATE, TIME or TIMESTAMP must be
CHARACTER.
The internal formats for the three types are
DATE CCYYMMDD
TIME HHMMSS
TIMESTAMP CCYYMMDDHHMMSSNNNNNN

Where Represents
CC Century
YY Year
MM Month
DD Day
HH Hour
MM Minute
SS Second
NNNNNN Microseconds
Example
05 WS-DATE PIC X(08)
VALUE SPACES.
05 WS-TIME.
10 WS-HOUR PIC XX
VALUE SPACES.
10 WS-MINUTE PIC XX
VALUE SPACES.
10 WS-SECOND PIC XX
VALUE SPACES.

20
Columns Accepting Null Values
When a column is defined to accept null values,
CA-Datacom/DB places a value in the null
indicator for the column when an application adds
a row to the table without supplying a value for
the column. Nil Values A null is not a nil
value. A nil value is a character blank (X'40')
or a binary zero (X'00'), which CA-Datacom/DB
treats as non-null values. The KEY attribute
INCLUDE-NIL-KEY determines whether CA-Datacom/DB
indexes rows with nil values for the key. A key
has a nil value when all of the columns in it
have the same nil value.
21

How to Define Columns to Be Unique?
Specifying that a column (or group of columns) be
unique ensures that each value in the column
exists only once in the table.
To be defined as unique, a column or group of
columns must not exceed 180 bytes in length.
To define a column as unique, define a
single-column key, specifying
Yes for the KEY attribute UNIQUE
Yes for the KEY attribute INCLUDE-NIL-KEY
No for the FIELD attribute NULL-INDICATOR

When an application attempts to add a row
containing a
duplicate value for a column or columns defined
as
unique, CA-Datacom/DB does not immediately reject
the add if the existing row is not committed. If
the value
is committed as present, CA-Datacom/DB aborts the
row add and issues the CA-Datacom/DB return code
94
(internal return code 193). If the value is
committed as
absent, the add continues.

23
Inserting and Accessing Records

The value of the key column MUST be provided
during an insert for CA-
Datacom/DB to correctly place the new record.
CA-Datacom/DB takes the value and manipulates it
to obtain the block
number where the record should go. This block is
read and CA-
Datacom/DB indexes into the block to the correct
physical location. If the
space has no RCE(Record Control Element which is
4bytes long), the
record is added. If an RCE exists, the add
fails with a duplicate unique
key. The first two bytes of the RCE must be the
length of the data record.
The third byte of the RCE must be the binary
table ID. The last byte in the
RCE must be a binary zero.
The key value presented is converted into a block
number
and record within block. This block is read and
CA-Datacom/DB positions
to the record. If no RCE is found, the return
code is 14.

CA-Datacom/DB Return Codes CA-Datacom/DB passes a
return code to the Request Area of a program in
response to the program issuing a CA-Datacom/DB
command. CA-Datacom/DB also issues return codes
within CA-Datacom/DB messages. A return code of
blanks indicates successful processing of the
command. A non-blank return code indicates an
error . All non-blank return codes have one or
more associated internal return codes.
25

Example
10 AFB-REQ-RETURN-CODE PIC X(002)
VALUE SPACE.
88 AFB-GOOD-RETURN
VALUE SPACE.
88 AFB-TABLE-NOT-OPEN
VALUE '05'.
88 AFB-TABLE-NOT-OPEN-4-UPDATE
VALUE '06'.
88 AFB-DATA-AREA-FULL
VALUE '07'.
88 AFB-INDEX-FULL
VALUE '08'.
88 AFB-PREREQUISTE-NOT-FOUND
VALUE '09'.
88 AFB-DUP-MASTER-KEY-NOT-ALLW
D VALUE '10'.
88 AFB-MASTER-KEY-MOD-UPT-REJ
VALUE '11'.
88 AFB-RECORD-NOT-FOUND
VALUE '14'.
88 AFB-EXCLUSIVE-CNTL-DUPLICAT
E VALUE '18'.
88 AFB-END-OF-FILE
VALUE '19'.
88 AFB-ELEMENT-NAME-NOT-FOUND
VALUE '22'.
88 AFB-ELEMENT-SECURITY-CD-VIO
L VALUE '23'.

Steps used to retrieve data from CA-Datacom/DB
in an Appln program
Establishes communications with CA-Datacom/DB
using a User Requirements Table.
Issues CA-Datacom/DB requests using the Call
Stmt and checks the result.
Terminates communications with CA-Datacom/DB.
User Requirements Tables
A User Requirements Table controls the features
at the program level.
Defines which CA-Datacom/DB tables can be
accessed/updated by CA-
Datacom/DB commands .
It specifies what resources are necessary for the
successful execution
of a program, including additional resources
the program can need,
such as extra buffer allocations.

Access Using a User Requirements Table
The User Requirements Table is generated by a
macro assembly and is
either link-edited with your program or
dynamically loaded at execution
time. It contains an entry for each CA-Datacom/DB
table your program
Accesses.
The User Requirements Table must be opened before
your program
requests access to CA-Datacom/DB tables, and
closed after all requests
have been made.
You can specify in the User Requirements Table
that CA-Datacom/DB open the
User Requirements Table before control is passed
to your program, and close the
User Requirements Table when your program
returns control to CA-Datacom/DB.
Alternately, your program can open and close the
User Requirements Table itself
by issuing OPEN and CLOSE commands.

Eg..
//CSTMTL76 EXEC PGMK1CSTMTL,PARM'DBURTK1CSTMU1
, COND(0,NE)
//
//TOC DD DSNK1C.KFS.K1CSTMTS.K1CTOC2N,
// DISPSHR
//SPX DD DSNK1C.KFS.K1CSTMTS.K1CPRT2N,
// DISPSHR
//
//LASER DD DSNK1C.KFS.PRINTW.K1CSTMTL.K1CSTM0
2,
// DISP(NEW,CATLG,DELETE),
// UNITPRDPK,SPACE(TRK,(2250,150),RL
SE),
// DCB(RECFMFBA,LRECL255,BLKSIZE0)
//

Entry Macro (DBURTBL)
A DBURTBL macro is required for each
CA-Datacom/DB table to be accessed by
CA-Datacom/DB commands.
Example
DBURTBL
X
ACCESSRAN,
X
AUTODXCYES,
X
BYPOPENNO,
X
DBIDPOLICY,
X
ELMCHGNO,
X
GBMAXR255,
X
GETBLK15000,
X
SEQBUFS00,
X
SYNONYMNO,
X
TBLNAMAGT,
X
UPDATENO
EJECT

BYPOPENvalue
Indicates the processing of the table specified
in the TBLNAMparameter during
User Requirements Table open and close
processing,as follows
BYOPENNO means the table specified in the TBLNAM
parameter Is not
bypassed.
BYOPENYES means the table specified in the
TBLNAM parameter Is bypassed
during open and close processing.
Valid Entries NO or YES
Default Value NO

AUTODXCvalue
Valid Entries NO or YES
Default Value YES
AUTODXCNo means ,Do not automatically drop
exclusive control.
If NO is specified and the record is not updated
or deleted, the program
must release exclusive control.
AUTODXCYes means, Automatically drop exclusive
control established
by the previous command from the same Request
Area.
--------------------------------------------------
-----------------------------------------------
ACCESS RAN
Starting with Version 8.1, this parameter was no
longer required.

UPDATE value
Valid Entries NO or YES
Default Value NO
UPDATENo means, The program cannot update this
table and cannot
hold the rows under exclusive control.
UPDATENo means, The program can update this
table and can hold
the rows under exclusive control.

Start Macro (DBURSTR)
Eg
DBURSTR ABENDYES, YES, NO
X
CSECTKFBATCH, DBURTRR
X
MSTNAMDBSULST, NO DEFAULT)
X
MULTUSEYES, YES, NO
X
PRTY7, 7
X
PXXAREANO, YES, NO
X TXNUNDONO,
YES, NO X
WRITENO YES, NO
EJECT
PRTY 7 (default)
This parameter establishes the priority for all
CA-Datacom/DB requests
issued by the program after the User Requirements
Table is opened.
Valid Entries Integer value from 1
through 15

TXNUNDOvalue
Valid Entries NO or YES
Default Value NO
If the value is Yes means the transaction backout
option is in effect
for all update transactions against all the
tables declared in this
User Requirements Table.
If TXNUNDONo, it Specifies transaction backout
is not
operational.

End Macro (DBUREND)
Code one DBUREND macro per User Requirements
Generation
Macro set.
Example
DBUREND
X
SYSTEMOS,
X
USRINFOKFBATCH
CSECT
DC CL50'L1ABATU193/03/0111040698/06/16NONE
0000100001'
END

Issuing Requests
CA-Datacom/DB services are requested through the
call facility of the particular language you are
using. The entry point DBNTRY should be called
with the following parameters
User Information Block (required)
Request Area (required)
Work Area (optional)
Element List (optional)
Request Qualification Area (optional)
SYNTAX
CALL 'DBNTRY' USING USER-INFO
REQUEST-AREA
I/O WORK AREA
ELEMENT-LIST.

In a COBOL-Datacom program, ENTRY statement is
the first one
Following procedure division.
Example
PROCEDURE DIVISION.
ENTRY 'DBMSCBL'.
EJECT
0000-MAINLINE.
The default entry point called by CA-Datacom/DB
is DBMSCBL.
CA-Datacom/DB transfers control to DBMSCBL after
opening the
User Requirements Table. An alternate name can be
specified
with the USRNTRYname parameter.

CALL STATEMENT
Example
CALL 'DBNTRY' USING AFB-USER-INFO
AFB-REQUEST-AREA
I-AFB-TABLE
AFB-ELEMENT-LIST.
User Information Block is a 32-byte required
area, which can be used to
identify the requestor of CA-Datacom/DB
services. CA-Datacom/DB
does not require that any particular information
be placed in this area, but
it is suggested that the program name be placed
in the first eight
characters to aid in problem determination.
05 AFB-USER-INFO PIC X(032) VALUE
'K1CFINUP'.

CALL Syntax for Languages Other Than COBOL
Assembler uses a CALL macro, while PL/I and
FORTRAN use a CALL statement.
Using the DBNTRY entry point, provide the
appropriate User Information Block, the
Request Area address, the work area address, the
element list address, and the
Request Qualification Area address in the call.
Assembler Format
CALL DBNTRY,(userinfo,reqarea,wrkarea,elmlst,quala
rea)
PL/I Format
CALL DBNTRY(userinfo,reqarea,wrkarea,elmlst,qualar
ea)
DECLARE DBNTRY ENTRY OPTIONS(ASSEMBLER)
FORTRAN Format
CALL DBNTRY(userinfo,reqarea,wrkarea,elmlst,qualar
ea)

Request Area
Required area is used to specify requests made to
CA-Datacom/DB, and
then test the results.
You may even use more than one Request Area for
the same table. For
example, one Request Area might be used to
sequentially read an
employee table, and another to read the employee
record for each
employee's manager.
The Request Area minimum length is 76-characters.
Depending on the
command used, it is followed by one or two key
value areas, which can be
from 1 to 180 characters long each.

05 AFB-REQUEST-AREA.
10 AFB-REQ-COMMAND PIC
X(005).
10 AFB-REQ-TABLE-NAME PIC
X(003) VALUE 'AFB'.
10 AFB-REQ-KEY-NAME PIC
X(005) VALUE 'AFBK0'.
10 AFB-REQ-RETURN-CODE PIC
X(002) VALUE SPACE.
88 AFB-GOOD-RETURN
VALUE SPACE.
88 AFB-RECORD-NOT-FOUND
VALUE '14'.
88 AFB-END-OF-FILE
VALUE '19'.
10 AFB-REQ-INTRNL-RTNCD PIC
X(001).
10 AFB-REQ-DATABASE-ID PIC
S9(004) COMP.
10 AFB-REQ-TABLE-ID PIC
S9(004) COMP.
10 AFB-REQ-RECORD-ID PIC
X(005).
10 FILLER PIC
X(025).
10 AFB-REQ-COUNT-MAX PIC
S9(004) COMP.
10 AFB-REQ-IO-COUNT PIC
S9(004) COMP.
10 FILLER PIC
X(022).
10 AFB-REQ-KEY-VALUE.
COPY AFBRK0. .

Work Area
The work area is used with record update and add
commands to pass
the elements listed in the element list, in the
order listed, to CA-
Datacom/DB. The work area is also used, in
conjunction with record
retrieval commands, to receive those elements
back from CA-
Datacom/DB.
This area must be large enough to accommodate the
combined length
of all the elements specified in the element
list. If this area is too small,
record retrieval commands overlay whatever
follows this area.
Eg
01 I-AFB-TABLE.
COPY AFBTBL REPLACING TAG BY
I-AFB-.
EJECT

43
Element List The element list specifies which
data elements are to be retrieved, updated or
added. Eg 05 AFB-ELEMENT-LIST.
10 FILLER
PIC X(005) VALUE 'AFBE0. 10
FILLER PIC X(006) VALUE SPACES.
44

Command Code
The 5-character command name specifying the
operation to be
Performed.
ADDIT Adding records to a database .
CLOSE Closing User Requirements Table .
DELET Deleting records from a database.
GSETL Set to Starting Key(prerequisite command
to GETIT).
GETIT Sequentially retrieving elements from a
database.
OPEN Opening User Requirements Table.
RELES Releasing exclusive control of records.
UPDAT Modifying elements in a database.
COMIT Committing a transaction.

Command Code
UPDAT Modifying elements in a database.
REDKX/RDUKX Retrieving data elements from the
database using the exact key value.
REDnn commands retrieve elements without
exclusive control for
update. RDUnn commands retrieve elements with
exclusive
control for update.

ADDIT (Add Record)
ADDIT inserts a record into a specified table
RETURN CODES
Blanks THE COMMAND WAS SUCCESSFUL
05 TABLE NOT OPEN
07 DATA AREA FULL
10 DUPLICATE MASTER KEY NOT ALLOWED
08 INDEX FULL
DELET (Delete Record)
The DELET command deletes a record from a table
and deletes all keys
associated with the record. DELET also releases
exclusive control of the
record.

Before a record can be deleted, two conditions
must be met. The record
must be read with exclusive control, and the
table specified in this
command must have been defined in the User
Requirements Table as a
table which may be updated.
GETIT (Retrieve Next Sequential Record)
In a batch environment, GETIT retrieves records
sequentially from any
table in a database, sequenced by any valid key
name, starting with a key
value greater than or equal to a specified key
value. GETIT optionally
obtains exclusive control of a record.
The first GETIT for a table must be preceded by a
GSETL command.
GSETL retrieves no data. It specifies the table
name, key name, and key
value, obtaining positioning for subsequent
sequential processing.
Return code
22 ELEMENT NAME NOT FOUND

REDBR/RDUBR (Read Backwards)
REDBR and RDUBR return actual data elements from
a database by reading
the next record with the previous sequential
entry in the index. RDUBR
acquires exclusive control for update purposes.
REDBR does not obtain
exclusive control.
You identify the starting point at which to read
backwards by issuing any
LOCKX command or any REDKX/RDUKX command.
REDKG/RDUKG (Read Record Greater Than/Equal to
Key)
The REDKG/RDUKG command enables you to obtain the
first record in a
table that has a key value in the index greater
than or equal to the key value
requested.
RDUKG acquires exclusive control of the record
for update purposes. REDKG
does not obtain exclusive control.

REDKL/RDUKL (Read Key Less Than or Equal to Key)
Use the REDKL/RDUKL command to obtain the first
record in a table that has a
key value in the index less than or equal to the
key value specified in the request.
RDUKL acquires exclusive control of the record
for update purposes. REDKL
does not obtain exclusive control.
REDKR/RDUKR (Read Record in a Specified Range)
The REDKR/RDUKR command enables you to locate a
record within a specified
key value range.RDUKR acquires exclusive control
of the record for update
purposes. REDKR does not obtain exclusive
control.
The beginning and ending key values of the range
in a 360-byte key
Area has to be specified. REDKR/RDUKR uses these
two values as boundaries
and locates the first record within the range.