Moving Through the Database and Locating Records

In this section:

After entering SCAN, your current position is at the top of the database. FOCUS databases are not sequential databases with one data record following another; they consist of segments. Databases can have one or more segments. The segments may have multiple instances of data (a Monthly Inventory segment holding a date and a quantity might have six instances in June and twelve in December). The collected data instances for a particular set of related segments constitute a logical record in the database.

The concept of a current line pointer (common in most system editors) is replaced in SCAN by the concept of a current position in the database, which represents a set of data instances that form a connected path within the database. Instead of processing databases line-by-line, SCAN achieves a somewhat similar effect by approaching FOCUS databases in a top-down, left-to-right scanning sequence.

As we said, on entering SCAN, you are automatically positioned at the top of the database. You may move through the entire database, or specify a subset of fields to be edited (called a Show List or a subtree). Show Lists are created with the SHOW subcommand, and they contain the fields you name (plus any intermediate segments required by FOCUS to navigate from one specified field to another). An important concept when specifying Show Lists is that the data in the selected records must meet all of the criteria specified in the SHOW subcommand.
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What You See in SCAN Display Lines

When you display the contents of logical records in SCAN, each data field is identified on the screen by either its alias or the field name, whichever is shorter (and non-blank). Given the following Master File, the SCAN operation proceeds as shown below. 

FILENAME=CAR,SUFFIX=FOC
SEGNAME=ORIGIN,SEGTYPE=S1
  FIELDNAME=COUNTRY,COUNTRY,A10,FIELDTYPE=I,$
SEGNAME=COMP,SEGTYPE=S1,PARENT=ORIGIN
  FIELDNAME=CAR,CARS,A16,$
SEGNAME=CARREC,SEGTYPE=S1,PARENT=COMP
  FIELDNAME=MODEL,MODEL,A24,$
SEGNAME=BODY,SEGTYPE=S1,PARENT=CARREC
  FIELDNAME=BODYTYPE,TYPE,A12,$
  FIELDNAME=SEATS,SEAT,I3,$
  FIELDNAME=DEALER_COST,DCOST,D7,$
  FIELDNAME=RETAIL_COST,RCOST,D7,$
  FIELDNAME=SALES,UNITS,I6,$
SEGNAME=SPECS,SEGTYPE=U,PARENT=BODY
  FIELDNAME=LENGTH,LEN,D5,$
  FIELDNAME=WIDTH,WIDTH,D5,$
  FIELDNAME=HEIGHT,HEIGHT,D5,$
  FIELDNAME=WEIGHT,WEIGHT,D6,$
  FIELDNAME=WHEELBASE,BASE,D6.1,$
  FIELDNAME=FUEL_CAP,FUEL,D6.1,$
  FIELDNAME=BHP,POWER,D6,$
  FIELDNAME=RPM,RPM,I5,$
  FIELDNAME=MPG,MILES,D6,$
  FIELDNAME=ACCEL,SECONDS,D6,$
SEGNAME=WARENT,SEGTYPE=S1,PARENT=COMP
  FIELDNAME=WARRANTY,WARR,A40,$
SEGNAME=EQUIP,SEGTYPE=S1,PARENT=COMP
  FIELDNAME=STANDARD,EQUIP,A40,$
 
 scan file car
  SCAN:
 next
 COUNTRY=ENGLAND  CAR=JAGUAR  MODEL=V12X15E AUTO
 TYPE=CONVERTIBLE SEAT= 4 DCOST= 7427 RCOST= 8878 UNITS= 0
 LEN= 190  WIDTH= 66  HEIGHT= 48  WEIGHT= 3435  BASE= 105.0
 FUEL= 18.0 BHP= 241 RPM= 5750 MPG= 16 ACCEL= 7

Note: SCAN uses ALIAS names instead of field names when aliases are shorter. Use DISPLAY (or CRTFORM) to display complete field names. Fields WARRANTY and STANDARD are not shown, because they do not lie on the path.
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Identifying Data Fields in Scan

Some SCAN subcommands require that you specify particular data fields for the operation. LOCATE, for example, requires that you supply the data value for the target field. Within SCAN you can identify a data field in one of three ways:

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Ways to Move Through Databases

In this section:

In SCAN sessions you can move from one segment instance directly to the next, jump from a parent segment instance to the first descendant field, or jump directly to a specific record of interest based on selection criteria specified in your request (for a description of these techniques, see Subcommand Summary).

The examples in this section use the CAR database, mentioned in What You See in SCAN Display Lines. Enter SCAN, and then the subcommand:

SHOW COUNTRY CAR MODEL

This restricts the Show List to the first three segments of the database, as shown by this diagram:

The following schematic diagram shows how the data used in the examples is placed within the FOCUS structure:

There are six subcommands you may use to change the current position:
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TOP

TOP moves the current position to the top of the database.

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LOCATE

LOCATE moves the current position to the next record that fulfills certain conditions. Often, you use LOCATE to find a record with a certain value. For example, if your current position is near the top of the database and you enter the subcommand 

LOCATE CAR=MASERATI

the following record appears:

COUNTRY = ITALY  CAR= MASERATI
                 MODEL = DORA 2 DOOR

If you enter this subcommand again, SCAN searches for the next MASERATI record. Since there is only one MASERATI record, it moves the current position to the end of the database.
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TLOCATE

TLOCATE moves the current position to the first record in the database that fulfills certain conditions. Often, you use TLOCATE to find a record with a certain value. For example, if you enter the subcommand 

TLOCATE CAR=ALFA ROMEO

the following record appears regardless of where the current position was in the database:

ITALY  ALFA ROMEO  2000 GT VELOCE
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NEXT

The NEXT subcommand advances the current position to the next record. That is, it advances the current position one segment instance in the lowest segment in the Show List.

Suppose you entered SCAN to edit the CAR database and displayed the first record belonging to Italy by entering:

TLOCATE COUNTRY=ITALY

SCAN displays the following record:

ITALY  ALFA ROMEO  2000 GT VELOCE

You then enter the subcommand NEXT:

NEXT

The lowest segment in this example is the MODEL segment. The MODEL instance in the record (2000 GT VELOCE) is the first of three instances descended from the car ALFA ROMEO. The NEXT subcommand moves the current position to the next instance in this chain, displaying the record:

ITALY  ALFA ROMEO  2000 SPIDER VELOCE

If you enter the NEXT subcommand again, SCAN displays:

ITALY  ALFA ROMEO  2000 4 DOOR BERLINA

Now you are at the end of the MODEL under the instance ALFA ROMEO. If you enter the NEXT subcommand again, it moves the current position to the first MODEL chain under the next instance in the segment CAR. The next CAR instance is MASERATI. The record displayed is:

ITALY  MASERATI  DORA 2 DOOR

MASERATI has only one child instance, and it is the last car under the instance ITALY. If you enter the NEXT subcommand again, it moves the current position to the first MODEL chain under the next instance in the segment COUNTRY. The record displayed is:

JAPAN  DATSUN  B210 2 DOOR AUTO
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JUMP

The JUMP subcommand moves the current position to the next segment instance in the segment you specify. The segment must have at least one field specified in the Show List.

Move the current position to the first record in the ITALY chain by entering:

TLOCATE COUNTRY=ITALY

This displays the record:

ITALY  ALFA ROMEO  2000 GT VELOCE

Move the current position to the next car in the ITALY chain by entering:

JUMP CAR

Note: CAR is a field and not a segment name.

The following record appears:

ITALY  MASERATI  DORA 2 DOOR

Now return to the first record in the ITALY chain:

TLOCATE COUNTRY=ITALY

Jump to the next country in the database by entering:

JUMP COUNTRY

The following record appears:

JAPAN  DATSUN  B210 2 DOOR AUTO
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UP

The UP subcommand moves the current position to the first instance in the lowest segment in the Show List descended from the segment that you specify.

Move the current position to the model 2000 SPIDER VELOCE:

TLOCATE MODEL=2000 SPIDER VELOCE

This displays the following record:

ITALY  ALFA ROMEO  SPIDER VELOCE

Move the current position to the first ALFA ROMEO model by entering:

UP CAR

The following records appears:

ITALY  ALFA ROMEO  2000 GT VELOCE

Move the current position to the Maserati car:

LOCATE CAR=MASERATI

Move the current position to the first car in the ITALY chain by entering:

UP COUNTRY

The following record appears:

ITALY  ALFA ROMEO  2000 GT VELOCE
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Displaying Field Names and Field Contents

In this section:

To view up to 64 fields, specify the SHOW subcommand. The SHOW subcommand does not list records lacking instances (short-path records).

To review field contents, use either the DISPLAY or TYPE subcommand.
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TYPE Subcommand

At any point in a SCAN session, you may use the TYPE subcommand to display field names in a segment path (or those named in the SHOW subcommand, if one is in effect) and their contents for the current logical record (and/or several consecutive records).

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DISPLAY Subcommand

DISPLAY produces a vertical list showing the full field names followed by the data values for the current logical record. DISPLAY allows you to select the fields to be displayed, and may include fields residing in segments picked up for the subtree but not actually named in the SHOW subcommand. This displays only the fields named in the SHOW subcommand if one is in effect.

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Suppressing the Display

When moving through a database in SCAN with NEXT, JUMP, LOCATE, or TLOCATE, you automatically get a display of the contents of the next record unless you suppress the display. You do this by putting a period after the move keyword. Therefore, 

NEXT.

retrieves, but does not display, the next record.

It is usually preferable to suppress the displays when performing global operations that affect many records.
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Show Lists and Short-Path Records

If some segments lack data, it means that some logical records have missing segment instances. FOCUS discards short-path records when constructing the Show List.

Consider a subset of the CAR database. The subset has three segments with one field per segment (COUNTRY, CAR, MODEL). If you name all three fields in a SHOW subcommand, logical records that lack data in any of the specified fields are not selected for the subtree (they are short-path records).

The following example illustrates this. To run this example, enter the following commands as shown below. What you enter is in lowercase; computer responses are in uppercase.

scan file car
 SCAN:
show country car
locate country=france
 COUNTRY=FRANCE CAR=PEUGEOT
input car=renault
 SCAN:
type
 COUNTRY=FRANCE CAR=RENAULT

The example is as follows. The CAR database contains this data:

Country

Car

Model

.

 

 

.

 

 

.

 

 

France

Peugeot

504 4 DOOR

France

Renault

 

Italy

Alfa Romeo

2000 4 Door Berliner

Note that the French car Renault has no instances in the MODEL segment. A SCAN operation that names all three segments drops the logical record for Renault because Renault is missing instances in the MODEL segment, as follows.

show country car model
type 6
    COUNTRY=ENGLAND   CAR=JAGUAR       MODEL=V12XKE AUTO
    COUNTRY=ENGLAND   CAR=JAGUAR       MODEL=XJ12L AUTO
    COUNTRY=ENGLAND   CAR=JENSEN       MODEL=INTERCEPTOR III
    COUNTRY=ENGLAND   CAR=TRIUMPH      MODEL=TR7
    COUNTRY=FRANCE    CAR=PEUGEOT      MODEL=504 4 DOOR
    COUNTRY=ITALY     CAR=ALFA ROMEO   MODEL=2000 4 DOOR BERLINER

Note: In all of the examples in this section, user input is shown in lowercase; the FOCUS response is in uppercase.

To locate short-path records that will be dropped from a Show List, make a test pass through the database at the short-path level to see what is there before issuing the Show List for the edit operation. (This is highly recommended when adding new records to a database.) Thus, for the simple previous example, if you start by making a pass through the database selecting all records containing values for COUNTRY and CAR, you will find the Renault car.

show country car
type 6
    COUNTRY=ENGLAND  CAR=JAGUAR
    COUNTRY=ENGLAND  CAR=JENSEN
    COUNTRY=ENGLAND  CAR=TRIUMPH
    COUNTRY=FRANCE   CAR=PEUGEOT
    COUNTRY=FRANCE   CAR=RENAULT
    COUNTRY=ITALY    CAR=ALFA ROMEO

On the next pass, you add the MODEL segment and note that Renault disappears (due to the short-path). Knowing this, you refrain from adding a potential duplicate record for France and make a mental note to make another pass to update the short-path record with data for the MODEL segment.

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